What is meant by Orphan Lock and Orphan Sessions?

I have came across this term ***Orphan locks*** and ***Orphan sessions*** and I really have *no idea* what that is. I have tried to *search* it on *Google* and I still haven't got any useful info/results regarding what it mean. *All I get till now is that orphan locks are some kind of session locks which results in deadlocks after executing query or queries.* (please correct me if I get it wrong) *Can someone please explain this a bit ? What are Orphan Locks ? Are they the same as Orphan sessions ? How do they form and what they have to do with sessions ?* p.s: I am still newbie to this so I apologise if it sounds all too basic.