"Hicisteis" is the second-person plural form of the verb "hacer" in the preterite tense, which means "to do" or "to make" in Spanish. It is used primarily in Spain and refers to actions completed in the past by a group of people being addressed directly. In a sentence, "hicisteis" can be used to say, "Vosotros hicisteis la tarea," meaning "You all did the homework." This form is part of the Spanish language and is commonly used in informal contexts, particularly among friends or family in Spain.