This term actually isn't newaccording to Mirriam Webster, the first known use of "vibe" was 1967. Dictionary.com says that the association between "vibrations" and a source of positive energy goes back to 1983. In the '60s, the term "good vibes" was popular [as evidenced by the 1966 Beach Boys song "Good Vibrations"].
The word "vibe," as opposed to "vibes" or "vibrations," is used commonly today. If we want to get technical, "vibe" can be used as both a noun and a verb. When it's a noun, "vibe" describes the distinct emotional impression of a place, gathering, or even a person. It's the feeling you get after you leave, and you're reflecting [i.e. "that place had a spectacular vibe" or "this room has a weird vibe"]. When a verb, "vibe" means to kick back and hang out, or to get along [i.e. "she and I were vibing on our date"].
Or, you can say, "It's a vibe," referring to the specific emotional atmosphere or sensation you find yourself in.