Generally in ORM and OOP , a persistent object refers to an object that exists (or persists) in the database
Generally in ORM and OOP , a transient object is an object that has not been saved to DB yet
"My intuition is that transient properties would incurr less overhead than persistent properties because they do not need to be persistent and read from the database so converting them to persistent properties will likely only make things slightly worse"
from question "Do transient properties in grails effect memory usage of an application?"
"Memcache data lives in memory and isn t persistent so is for more transient data"
from question "How is JPA and Memcached different?"