A surrogate is someone who takes the place of another person or acts on their behalf.

In everyday use, a surrogate steps in when someone else cannot be present or fulfill a role. A teacher might ask a student to be her surrogate by delivering a message to the office. When your parents can't attend a school event, they might send a surrogate like your aunt or grandmother to represent them. The surrogate isn't the original person, but they're trusted to act in that person's place.

You might also hear surrogate used as an adjective to describe substitute measures or stand-ins. Scientists might use mice as surrogates for humans in early medical research. A coach might use practice scrimmages as a surrogate for real game experience. In each case, the surrogate stands in for something else while trying to serve the same essential purpose.