I need to know what language GREP is. I know its a search string command, but I need to know if it is its own language or what the deal is.

it's a UNIX command

Here's a good description
http://en.wikipedia.org/wiki/Grep

You can use Regular Expressions with grep, but it doesn't have it's own language.

Grep is based on the posix regular expressions (PERL compatible) and is written in C (ouch). Its not a bad utility and is easy to learn compared with other posix util languages like sed or awk (which are just as good as grep but much more usefull if you can learn the syntax of them).

I use it daily for all kinds of things.

Ibbo

It's great for piping things through it:

yourprog.exe | grep -i error

will run your program, and supress all command line output unless it matches the regular expression (in this case 'error')