A padded sports shoe ("trainer" is used commonly in British English where sneaker would be used in American English). The term "trainer" derives from "training shoe".
A person who is responsible for preparing a horse for races.
A person who guides another in developing physical fitness.
A trainer (business) who instructs a person or persons on a particular subject within a formal curiculum or other educational process or method; usually in a business context.
A hack of a ROM image that adds in extra options, usually to make the game easier.
An Athletic trainer is one who provides medical assistance to athletes or other physically active individuals. It is improper to refer to an Athletic Trainer as 'Trainer.'