A beret was a type of hat.

UNIT soldiers and officers alike wore berets in the field. Over the years, the standard-issue UNIT field beret changed from khaki brown, (TV: Spearhead from Space) to chocolate brown (TV: The Ambassadors of Death) to army green (TV: Terror of the Autons) to United Nations blue (TV: Battlefield) to crimson. (TV: Aliens of London) In Donna's World, UNIT berets were raven black. (TV: Turn Left)

Sarah Jane Smith wore a cherry beret during her last adventure with the Fourth Doctor, (TV: The Hand of Fear) and her reunion with the Third Doctor in the First Rani's trap. (TV: Dimensions in Time)

Sergeant Paterson wore a raven black beret during the Tremas Master's Survival Stratagem and his encounter with Cheetah People. (TV: Survival)