An English idiomatic expression with the basic meaning of, yes, I'll try it.
Usually said to agree to something one has never experienced before, and is agreeing mostly out of curiosity, or to learn something new.
For example, if one is invited to a Thai restaurant, while one has never eaten Thai food and has no idea whether one is going to like it, but is willing to try it just for the heck of it, one might reply "I'm game."