Pictionary is a popular party game where one player selects a word and then tries to get their teammates to guess the word by drawing pictures on a whiteboard within a time limit, without using words or letters. Players take turns being the artist who draws clues for their team or being guessers who try to correctly identify the word or phrase the artist is depicting based solely on their picture clues. The game is fun and challenging as it encourages creative thinking and visual communication skills without words.