Solidity concepts

Concept / Keyword	Description
Visibility	Specifies the accessibility of functions and state variables: public, internal, external, private.
State Variables	Variables that hold data persistently across function calls within a contract.
Events	Mechanism for emitting and logging occurrences within a contract, often used for backend services.
Modifiers	You can define modifier and reuse it in functions. (e.g. ownerOnly)
Inheritance	Feature allowing contracts to inherit properties and methods from parent contracts by using is keyword.
Libraries	Collections of reusable Solidity code that can be deployed independently and linked to other contracts by using library in the source contract and import keyword in the sub contract.
Structs	Custom-defined data structures allowing grouping of related data under a single name.
Enums	User-defined types with a finite set of possible values, useful for defining state transitions and options.
Arrays	Data structures allowing storage of multiple values of the same type under a single variable name.
Mappings	Key-value stores allowing efficient storage and retrieval of data based on unique keys.
Error Handling	Techniques for managing exceptions and errors in Solidity, including revert, require, and assert statements.
require	Statement used for validating conditions within functions, reverting execution if conditions are not met.
Memory Variables	Function variables that require explicit declaration of the memory type for temporary storage.
msg Structure	Special global variable providing information about the current transaction, including sender and value.
block Structure	Special global variable providing information about the current block, including timestamp and difficulty.
Solidity Assembly	Low-level language for interacting with EVM directly, allowing fine-grained control over contract execution.
View and Pure Functions	Functions that promise not to modify state (view) or read from state (pure), enabling optimizations and clarity.
Interface	Blueprint for other contracts to follow, specifying the functions and events that must be implemented.
Fallback Function	Special function invoked when a contract receives Ether without a specific function call.

If you think that any other concepts should be remembered, please leave a comment below.