like:

3 ≠ 4

the equal would have a slash through it because 3 IS NOT equal to 4.

RE:
Math question: what is the little equal sign with a slash through it called, and what does it mean?
I am doing my homework and my teacher never really told us it…somehow all the other kids already knew it.

It means “is not equal to”. The slash is used to negate other signs as well, for instance a < sign with a slash through it means "is not less than". Generally any sign with a slash through it means the opposite of the same sign without the slash. In text forums it can be written as /= or =/ but is also often written in these forms, which derive from computer programming languages: != and <>.