📘 Expert-Level Vocabulary for System Design & Software Engineering Interviews

This document is your ultimate guide to sounding like a seasoned engineer in high-stakes system design and software engineering interviews. It includes terminology, definitions, real-world context, and example phrases that help you articulate technical solutions with clarity, depth, and impact.

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🔹 1. Core Software Engineering Principles

Term	Meaning	Example Use
Abstraction	Reducing complexity by hiding implementation details and showing only essential features.	"We abstracted the file system interaction into an interface so it could be mocked during unit testing."
Encapsulation	Keeping internal object details private and exposing only necessary parts.	"Encapsulation helped us prevent accidental modification of critical state."
Modularity	Dividing a system into interchangeable and manageable components.	"Our codebase uses modular design to allow parallel development across teams."
Cohesion	Measure of how closely related responsibilities of a single module are.	"High cohesion in our classes led to better readability and maintainability."
Coupling	Degree of interdependence between software modules. Low coupling is better.	"We reduced coupling using dependency injection."
DRY (Don't Repeat Yourself)	Avoid duplicating logic; extract shared code into functions or classes.	"Following DRY helped eliminate 300 lines of redundant code."
KISS (Keep It Simple, Stupid)	Prioritize simplicity in design.	"We avoided unnecessary complexity by adhering to KISS."
YAGNI (You Aren’t Gonna Need It)	Don’t build features until they are needed.	"We dropped the advanced caching layer due to YAGNI."
SOLID Principles	Five object-oriented design principles.	"We applied the Single Responsibility Principle to split the UserService class."
Refactoring	Improving code structure without changing behavior.	"Refactored our monolith into smaller services to improve scalability."
TDD (Test Driven Development)	Writing tests before writing code.	"Our CI/CD pipeline enforces TDD with 80% code coverage."

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🔹 2. System Design Essentials

Term	Meaning	Example Use
Latency	Time delay between a request and its response.	"We optimized network calls to reduce latency by 20ms."
Throughput	Number of transactions or requests handled in a given time.	"Redis caching helped increase our throughput under peak load."
Scalability	Ability of a system to grow and handle increased demand.	"We horizontally scaled our read replicas to meet traffic spikes."
Availability	System's uptime or readiness to serve.	"We achieved 99.99% availability via active-passive failover."
Reliability	System's ability to function correctly over time.	"Service retries and error handling boosted our system's reliability."
Fault Tolerance	Ability to continue functioning when components fail.	"The system uses retry queues and circuit breakers for fault tolerance."
CAP Theorem	Consistency, Availability, Partition Tolerance—pick any two.	"We favored availability and partition tolerance over strong consistency."
Idempotency	An operation can be repeated with the same effect.	"PUT and DELETE operations were made idempotent to support retries."
Backpressure	Managing load by slowing producers when consumers are overwhelmed.	"We used Kafka's built-in backpressure handling for safe ingestion."
Rate Limiting	Restricting request rate to prevent overload.	"Implemented rate limiting using a token bucket algorithm."
Caching	Storing data temporarily to reduce recomputation or network calls.	"Used Redis to cache frequent queries and improve latency."
Sharding	Splitting data across servers based on a shard key.	"User data was sharded by region to improve query performance."
Replication	Copying data to multiple nodes for redundancy and performance.	"We used master-slave replication with automatic failover."
Eventual Consistency	Updates will propagate and become consistent over time.	"Our S3-based system achieves eventual consistency across regions."

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🔹 3. Architecture Patterns & Styles

Pattern	Meaning	Real-World Context
Monolith	All components in a single codebase.	"Our initial MVP was a monolith for faster iteration."
Microservices	Modular services communicating over APIs.	"We decomposed the monolith into microservices to scale better."
Event-Driven Architecture	Services react to and emit events.	"Order processing is triggered via Kafka events."
CQRS	Split read and write models.	"We used CQRS to optimize read-heavy dashboards."
Serverless	No server management; functions run on demand.	"Used AWS Lambda for lightweight, infrequent jobs."
Service Mesh	Infrastructure layer to manage service communication.	"Istio helped enforce security and observability across services."
Hexagonal Architecture	Core logic is decoupled from external inputs/outputs.	"Using hexagonal design allowed us to easily replace our DB layer."

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🔹 4. DevOps, CI/CD & Deployment

Term	Meaning	Example Use
CI/CD	Automated integration and deployment of code.	"Our CI/CD pipeline runs on GitHub Actions and deploys to Kubernetes."
Blue-Green Deployment	Switching traffic between two environments to release safely.	"Reduced downtime by adopting blue-green deployment."
Canary Release	Gradually exposing new versions to a subset of users.	"Rolled out new feature as a canary to 5% of traffic."
Infrastructure as Code	Defining infra via code (e.g., Terraform).	"Provisioned VPC and EC2 instances using Terraform scripts."
Immutable Infrastructure	Servers are never modified post-deploy.	"Used AMIs to create immutable app servers."
Observability	Monitoring via metrics, logs, and traces.	"We added distributed tracing for full request visibility."
Auto-Scaling	Adjusting compute resources dynamically.	"Enabled auto-scaling in Kubernetes to handle load changes."

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🔹 5. Databases & Storage

Term	Meaning	Example Use
ACID	Guarantees for transactions in RDBMS.	"Ensured consistency with ACID-compliant MySQL transactions."
BASE	Weaker consistency model for NoSQL.	"Cassandra follows BASE for better availability."
Normalization	Reducing redundancy in relational DB design.	"Normalized schema reduced data anomalies."
Denormalization	Intentional redundancy to optimize reads.	"We denormalized tables to support analytical queries."
Sharding	Partitioning data across nodes.	"MongoDB sharded collections by user_id."
Indexing	Boosting read performance with search indices.	"Added composite index for faster multi-column queries."
OLTP/OLAP	Operational vs analytical DB systems.	"OLAP cubes were built on Redshift for business reporting."

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🔹 6. Networking, Security & Protocols

Term	Meaning	Example Use
DNS	Resolves domain names to IP addresses.	"Configured custom DNS for internal microservices."
CDN	Distributes content close to users geographically.	"Used Cloudflare as our CDN to serve assets globally."
TLS/SSL	Encryption for secure communication.	"Enabled TLS termination at the load balancer."
JWT	Secure token for user identity.	"Used JWTs for stateless authentication."
OAuth 2.0	Framework for authorization.	"Integrated OAuth 2.0 with Google SSO."
Zero Trust	Always verify; never trust by default.	"Adopted Zero Trust for all internal services."

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🔹 7. High-Impact Expert Phrases

Phrase	Why It Works
"We prioritized latency-sensitive paths using edge caching."	Demonstrates performance sensitivity.
"Our design ensured eventual consistency with compensating transactions."	Shows knowledge of distributed transactions.
"We implemented graceful degradation under heavy load."	Indicates robustness planning.
"Backpressure strategies ensured system stability during bursts."	Reflects maturity in architecture.
"We decoupled services using an asynchronous message broker."	Speaks to modular, scalable design.
"We optimized for read-heavy workloads using CQRS."	Highlights optimization skill.

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✅ Next Steps

• Memorize with context: Use flashcards or Anki.
• Practice usage: Use these terms during mock interviews.
• Read real-world postmortems and blog posts from Netflix, Uber, etc.