Very large scale integration or VLSI is when lots of tiny electronic parts called transistors are put together on a teeny, tiny microchip to make a really complicated computer or electronic device.
Imagine you have a bunch of Legos. If you put them together just right, you can make a really cool spaceship or castle. VLSI is kinda like that, but with electronic parts instead of Legos.
Now imagine that you need more than just a spaceship or castle- you want a whole city with lots of buildings and people. Instead of trying to make each building and person separately, you can use VLSI to create lots of tiny microchips that can do lots of different things.
These microchips can be put together to make computers or electronics that are really powerful and can do lots of different things, just like a city with lots of different buildings and people!