Pet carriers are small portable boxes/cages used to transport small animals such as cats, lap dogs, guinea pigs (etc...) from one location to another. The two main types are the front openers (these are generally tough plastic boxes with a metal door) and top openers (theses are generally more like cages with a hinged roof), although there are other types. There is a handle on top of all types, although some are easier to carry in your arms rather than using the handle.