Zone out is a phrase used to refer to one's mental state when they become lost in thought or lose focus on a particular task or activity. There are several synonyms for this expression, some of which include spacing out, daydreaming, staring into space, drifting off, and tuning out. Each of these expressions can be used interchangeably to depict someone who has become detached from their surroundings or has temporarily lost focus, either by choice or due to factors such as boredom or fatigue. It's important to recognize when you're zoning out and take the necessary steps to regain focus when needed, especially in situations that require your undivided attention.