Oomph is an exciting, energetic quality in a person. If you don't have enough oomph, it will be hard to talk your classmates into voting for you for student council president.
The informal noun oomph is a good way to describe a certain aspect of someone's personality that resists being named. If you've got oomph, you're spirited and lively — you could say you've got moxie or pizzazz. Sometimes the word describes a specific kind of attractiveness or desirability: "My brother says he likes that actress because of her oomph." This word dates from the 1930s.