Literally means pus in the womb. This is rare in cats because most cats are spayed i.e. have the ovaries and womb removed early on in life. It is usually a disease of middle aged to older bitches most of which have never been bred.
It follows on from a season and comes in two basic forms – open where the cervix allows pus out to be seen, and closed where the pus is kept in the womb by the cervix being closed. A closed pyometra is usually more serious than an open one, and is obviously less easy to diagnose. Open pyometra is an easy diagnosis - the pus can be seen. Closed is less easy although there is a typical picture of the older bitch, recent season, drinking a lot and becoming very poorly indeed to help with diagnosis.
Surgery is the treatment option of choice, is highly successful and very satisfying to do.