I always thought of a utility player as the girl that plays her position best, but can suit the team better in another position. IE: girl is great at second but the right fielder is getting killed, drop her back and she doesnt miss a step, or complain, to help the team.
She will always be on the field, you just dont know where. She will always make a difference in one way or another.
Wikipedia defined as: READ THE LAST LINE
In baseball, a utility player is a player who can play several different positions.
In general, each major league baseball team has at least one player who can be described as a utility player. The most famous utility player is probably Pete Rose (though he was not described as such), because during his career, he played left field, right field, center field, third base, second base and finally, first base late in his career. A famous current utility player is Ryan Theriot of the Chicago Cubs, who despite now being their starting shortstop, has played shortstop, third base, second base, and outfield at some point in his short major league career. As well as the Detroit Tigers third baseman Brandon Inge who has played third base, shortstop, second base, catcher, left field, right field, and centerfield. Most professional teams have two types of utility players. There are "utility infielders", who usually play all of the infield positions (plus occasionally catcher). Utility outfielders, or fourth outfielders, tend to play all three outfield positions as various times. Occasionally, there will be players who perform a combination of the two duties. Utility players tend to be players who come off of the bench, though this isn't absolute. Often, players who don't have high prospects to be a major league star will learn additional positions so they can look more attractive to major league clubs as bench talent.
Cookie Rojas, Bert Campaneris, Shane Halter, and Jose Oquendo all played every position (including pitcher) during their respective careers.
Tony Phillips was the first player to start 10 games at five different positions in the same season.
In softball, a utility player is a player who can play several positions but can also bat well. Coaches often look for such players to bat as clean-up or 5th in the lineup.