What Is a Memory Leak?

Anything that runs on your computer or phone needs memory to work.
On a computer, we have two main types of memory:

RAM (Random Access Memory) – temporary, fast, used while apps are running.
Hard drive (or SSD) – permanent storage for files and apps.

When your RAM gets full, your system may start using the hard drive as slower “virtual memory.”
On mobile devices, it’s similar — there’s RAM (for running apps) and internal storage or memory card (for saving files).

How Memory Works in Apps:

When you open an app, it loads images, data, and resources into RAM so it can run quickly.
In an ideal world, when you close the app — or move from one screen to another — it should free up the memory it used, since it no longer needs that data.

But that’s not always the case...

What Is a Memory Leak?

Imagine you invite a friend to stay at your house for one night — but she decides to live in your room forever.
That’s what a memory leak is.

The app borrowed some memory temporarily, but instead of letting it go, it keeps holding onto it even when it’s no longer needed.

Over time, the app’s memory usage keeps growing.
Eventually:

The app becomes slower

The phone heats up

Or it crashes with “out of memory” errors

Why It Happens

Memory leaks usually occur when developers forget to:

Remove event listeners

Clear timers or intervals

Release references to images, arrays, or objects no longer needed

For example:

useEffect(() => {
const interval = setInterval(fetchData, 5000);
return () => clearInterval(interval); // cleanup to prevent leaks
}, []);

Or when large objects are kept in memory:

const bigImage = loadImage('banner.png');
// ... app closes, but bigImage is still referenced somewhere

How Developers Prevent It:

Developers use profiling tools to detect leaks — like:

Android Studio Profiler

LeakCanary

Flipper (React Native)

They also:

Clean up listeners and intervals in useEffect

Release images and cache data properly

Move heavy data to the server, not the client app

In Short:
A memory leak is when an app refuses to let go of the memory it once borrowed.