What does it mean to get your hair Layered?

I’ve recently been styling my hair when it gets long and it’s going great, but now it’s getting fairly long and thick so I’m planning on getting it trimmed and thinned. But, I saw someone say something about getting your hair layered as well. What’s that mean? I mean, It kinda seems straightforward to me I guess, but can anyone explain exactly what it is? I’d search more into it but I’m off to bed now.

Cheers.