Simple Definition:

Depersonalization is a psychological [related to the mind or mental health] condition in which a person feels detached [separated or disconnected] or disconnected from their own thoughts, feelings, and identity, or from their body.

For example, someone with depersonalization may feel like they are watching themselves from outside their own body, or like they are in a dream and their experiences [things that happen to them] aren’t real.

Very Simple Definition:

Depersonalization is when someone feels like they are not connected to themselves or their experiences.

For example, it could be a feeling like you are watching a movie of your own life instead of actually living it.