From BR Bullpen
A utility player or utility man is a player who can appear at several different positions. Such players are prized for their roles on the bench, especially in the modern era of large pitching staffs and reduced benches. A player like Rob Mackowiak can back up at several positions, giving managers flexibility in using their substitutes. There are also more specifically utility infielders, who back up usually at second base, shortstop and third base - players like Randy Velarde have filled this role for years. Occasionally, a utility player will be so effective, such as Tony Phillips, that they get a regular spot in the lineup for years to come without ever holding a position as a regular. The term is sometimes used to refer to any backup position player, but this is a far less common usage.