What's a scalable code?

Scalable code is code that can handle growth, like more users, more data, or bigger problems, without needing to be completely rewritten.

Let me explain with a simple example:

Imagine you're building a house using LEGO blocks.
At first, the house is built for a small family of four, so just a few blocks are enough.

But what if the family grows?
If you’ve made the house scalable, you can add more rooms and floors just by snapping on more blocks.

However, if it wasn’t built with that flexibility, you'd have to tear the whole thing down and start over, which takes time and effort.

Similarly in coding:
If your code was originally designed to handle 100 users, and tomorrow that grows to 1,000 or even 100,000, you should be able to scale it up smoothly, without rewriting everything from scratch.