What is the effect of the figure of speech used in the sentence the dancer glided like a swan?

The figure of speech used in this sentence is a simile.

A simile compares two things using the words "like" and "as"

In this sentence, the simile is being used to provide the characteristic of the dancer as to how they are gliding.

In other words, the simile is describing how the dancer was gliding.

Extra:

A simile may at times be confused with a metaphor which is the same thing as a simile however metaphors do not use the words "like" and "as".

bevy means a large group or thing of a certain kind.