1. To lose focus or stop paying attention to something, usually unintentionally. The term can be used to indicate that someone has focused on one thing to the exclusion of all other stimuli. I think I must have zoned out during that lecture, because when it was over I realized I didn't remember anything the professor said. Jerry kind of zones out when he plays video games, so you have to be really loud to get his attention.

2. To intentionally ignore or block out certain stimuli, distractions, etc. In this usage, a noun or pronoun can be used between "zone" and "out." When you're playing, you have to zone out everything except what's happening on the field. I know Aunt Lula can be aggravating, but she's only here for a few days, so just try to zone her out.