Bacterial vaginosis is an infection of the vagina caused by bacteria. Normally, there are a lot of "good" bacteria and some "bad" bacteria in the vagina. The good types help control the growth of the bad types. With bacterial vaginosis, the balance is upset. There are not enough good bacteria and too many bad bacteria. This can cause a discharge from the vagina that may smell fishy.
The infection may go away on its own in a few days. Antibiotics can help.