What does the COS button on my scientific calculator stand for?

It’s the cosine button.

yes I know it’s co-sign but what does it mean?

Well, you asked what the COS button stood for, didn’t you?
Here.

Not co sign, cosine. It is a trigonometric function used for many applications within algebra, geometry, trigonometry and other areas of math and science. Search it on google and you will be provided with many helpful articles about it.

AC’s article is very helpful too.

thank you :)

to add to Eambos’s post, trigonometry is also used in more advanced mathematics such as Calculus and is absolutely necessary in physics.

A bit off topic but it reminded me of my favorite nerd cheer.

SINE! COSINE!
COSINE! SINE!
3.14159!

I taught my math teachers that every year. God bless 3rd Rock from the Sun.