So in simple words, a blockchain can be compared to a train. The way that a train has bogies connect to each other in the same way there are blocks connect to each other, once a boogie is disconnected from the main train, all bogies after that are left behind, and in the same way if a certain block has been tampered all the blocks after that block become useless and corrupt!
This is what a blockchain is in layman language!
Here is the main definition of the blockchain:-
A blockchain is, an immutable time-stamped series record of data that is distributed and managed by a cluster of computers
Blockchains can be a very useful way of storing information because of its decentralized approach! By using this kind of approach no can really remove any data or add any data, this can help us in storing many confidential data without having a fear of it being tampered with
One of the very positive sides of the blockchain is its decentralized approach, this kind of approach keeps the data in the blockchain away from a single entity and we can rest assured that the data safe!
They allow anyone to participate as users, miners, developers, or community members. All transactions that take place on public blockchains are fully transparent, meaning that anyone can examine the transaction details.
Another type of chain is private blockchains, also known as permission blockchains, which possess a number of notable differences from public blockchains.
This means that it combines the privacy benefits of permission and private blockchain with the security and transparency benefits of a public blockchain. That gives businesses significant flexibility to choose what data they want to make public and transparent and what data they want to keep private.
Privacy is one of the most important things in a human's day to day life if your data is not secure/accessible by others then it is a very concerning thing for you as a human being in this digital age. And to tackle this thing there is a new technology called blockchain it keeps your data secure and the best of all none governs it so your data is completely anonymous.
For more detailed info
What Different Types of Blockchains are There?