The above mentioned rave vibe has moved into general use in the internet crowd. In the most general sense a vibe refers to the emotional tone of a place, group, person, website, or whatever else. A vibe is felt intuitively and typically resists analytical examination. Vibes can be good or bad, friendly or off putting, energetic or mellow and may be detected by some while being completely absent to others. The vibe of a place and the feel of a place are basically interchangeable though vibe has slightly more essentialist connotations. A vibe taken in a general sense can refer to an aesthetic absent any instantiation.
The other modern usage is as a verb. It can be used one of two ways. To vibe in isolation just means to chill or relax. It has a slightly more deliberate and active connotation than either but it basically means to have a good time in a mellow fashion. If someone is vibing with something or someone else they are involved in some positive emotional way. This can mean having an engaging conversation, feeling the message of a song, liking the atmosphere in a video game, or just enjoying people watching at a park.
Obviously, vibe in all of its incarnations has been short for vibrations. We've long attached musical language to things felt and nebulous and vibes appear to be just one more example of this tendency.
IRON NODER XVI: MORE STUBBORN-HARD THAN HAMMER'D IRON