It means "proceed" but can have other meanings in particular contexts. For example, there is a famous line from an American movie, "Go ahead, make my day!" In this context, "go ahead" still means "proceed" but not in the sense of giving someone permission. Rather it means "proceed if you dare" or "proceed if you must." Sometimes native speakers will also say "go right ahead." Example: "I want to start eating my dinner, the food is getting cold." "Go right ahead."

Go ahead is a phrasal verb which means to proceed or to start something, it is usually used when someone is giving you permission to do something or they are advising you to do something for example: a) May I use your bathroom please? b) Yes of course, go ahead, do you know where it is? Or - Please go ahead and eat, don't wait for Tom, he's always late. Hope it helps:)

well I think " go a head " is keep doing.

Go straight. I think "go ahead" and "go straight" mean the same.