Question about meditation

I have a question about meditation. What is it and what is it for? I hear a lot about what it's not. It's not about going into a trance. It's not about gaining insights into the universe. Okay then, what IS it? What can I get from it?

This might sound kind of silly but the Vulcan version of meditation from the various versions of Star Trek does kind of make sense to me. Tuvok describes how one can use visualization to control your internal functions. Your emotions, your concentration etc. You visualize the problem then you dissolve it. Make it float away in a puff of smoke or something. Is that at all related to any Earthly meditation practices? From the little I know about it, I guess you're just supposed to sit there. Which frankly, makes me wonder about its legitimacy. What is its function?