Anxiety:

A feeling of worry, nervousness or unease, typically about an event or something with an uncertain outcome.

That's the dictionary definition of anxiety.

But in reality it's the panic attacks about doing something or being around someone. It's the heart beating so fast that when you try to count them you miss a beat.

It's the feeling of a bottomless pit in your stomach, the feeling of nausea like you're going to puke your stomach out.

The feeling of your whole body shaking like a cat after a bath.

Not being able to get your lips to move to form a single word. 

Your mind is racing like a nascar. 

Not being able to get your lungs enough air to be able to breathe

It's the doctors telling you there is something wrong with you and gives you drugs to make it all “better”

The society telling you you're faking it because you want attention 

Your parents thinking you're the boy who cried wolf because you're only ten years old 

Anxiety 

Not just the definition but everything in between.