Lapse can be a noun or a verb, and it means:
* (noun): A temporary failure of concentration, memory, or judgment.
* (verb): To fall into a state of inactivity or disuse; to cease to be in effect.
Lapsed is the past participle of the verb lapse, meaning "having fallen into a state of inactivity or disuse".
For example:
* Lapse of memory: "I had a lapse of memory and forgot where I parked my car."
* Lapsed membership: "He was a lapsed member of the club, meaning he had stopped paying his dues."