Curly Braces?

Forgive me if this is a dumb question...

I've been seeing people store data in a field with {}. For example, Wordpress uses it for wp_user_roles in the options table: a:5:{s:13:"administrator";a:2: ...

I'm not even sure what it's called, or how/when/why to use them? I've googled it, but, ah, lacking the name for it closes many doors for me.

If somebody could point me in the right direction, that would be really great!

I'm looking to condense some tagging, and figured this might help.

Thanks!