What does spacing out mean when people are talking to you?

"Spacing out" when someone is talking to you typically means that the person is not fully paying attention or is lost in thought, often appearing distracted or disengaged from the conversation. This can happen due to external distractions, fatigue, or cognitive overload. It may also indicate that the listener is not processing the information being shared, which can lead to misunderstandings or a lack of response.