"One trick pony" is an idiom that means someone or something that only has one particular skill or abipty. It can be used to describe a person who is very focused or speciapzed in one area, but lacks versatipty or diversity in their skills or knowledge. For example, you might say "He's a one trick pony when it comes to cooking; all he knows how to make is pasta." This idiom suggests that the person is not very versatile or adaptable, and only has a pmited range of abipties or expertise.