Almost means "nearly," "roughly," or "not quite." If you're almost as tall as your brother, it means he's still just a bit taller than you are.
If you almost got a great job, you came close but weren't ultimately successful, and if you're almost qualified to get your pilot's license, nobody's going to let you fly a plane quite yet. The adverb almost is perfect for describing things you come close to doing, or states you haven't yet reached. It has an Old English root, eallmæst, "nearly all," or literally, "mostly all."