A vibrator is an electric device that shakes quickly. The shaking is the whole point of the machine — it is not a fault. There are two very different everyday meanings, and you should know both. First, in massage and physiotherapy, a vibrator is a small machine you hold against the back, shoulders or legs; the fast shaking loosens tight muscles. Second — and this is much more common in ordinary conversation — a vibrator is a sex toy used for sexual pleasure, usually by women. Because the second meaning is so well known, saying this word in a normal conversation will usually make people think of that meaning, even if you meant the massage machine. So most people now say 'massage gun' or 'massager' for the muscle one. There is also a technical use in engineering: a concrete vibrator is a tool that shakes wet concrete so the air bubbles come out. If you are speaking about that, the context makes it clear. This is a normal, non-rude word — it is not a swear word — but it is a private-life topic, so people say it quietly or choose another word in class, at work, or with older relatives.