What does fluid in the ear mean in an adult?

Same as a child: It is fluid behind the ear drum as a result of congestion of the eustachian tube and backed up fluid. Can cause mechanical decrease in hearing. Will clear. Chiropractic and craniosacral therapy or osteopathic adjustments will help a lot.

Middle ear fluid: Needs to get checked. As we get older, the middle ear bones get more brittle and are more easily eroded by middle ear fluid. Could be caused by a problem in the nose or more specifically in the nasopharnx. See an ENT doctor so you can learn why you have this and how you can treat!