I think here is a basic definition of it with some illustration:
What is Blockchain?
How Blockchain Works?
I think it is wonderfully shown on the picture below:
Source
What is Blockchain?
- It is like a database duplicated thousand of times across a network of computers, in which the network of computers have access to the database at the same time to regularly update the said database;
- Information are shared (and continually reconciled) throughout the whole network; and
- Data are accessible to anyone - no centralized version exists for hacker to target to corrupt.
How Blockchain Works?
I think it is wonderfully shown on the picture below:
Source