According to the Ringling Brothers Clown College, clowns must possess the following abilities (which defines their expected description).
Clowns must be able to interact with a crowd and be humorous. This is learned through exercises where the clown learns how to mirror and improvise.
Clowns must be able to juggle. Not only does this entertain the crowd, juggling shows physical athleticism, coordination, and flexibility.
Like juggling, balancing is a necessary talent for clowns. Again, this shows their athleticism, coordination, and flexibility.
Each clown is required to create a persona. A persona is the character the person plays as the clown. Some clowns are known for specific facial expressions, color of costuming and makeup, and acting (for example, sad or happy clowns).
Clowns are an integral part of the circus. Therefore, they must have exemplary knowledge of the terminology associated with the circus.