Early in Bitcoin users called these things "orphan blocks" because when they were the miner of the blocks the coinbase payment to them would show as "orphan" in the wallet.  But it wasn't the block that was orphan, it was the transaction-- the transactions parent block no longer existed in the wallet's view of the chain.  Some people complained about the use of the term "orphan block" because that term was already in use in side the software for blocks whose parent wasn't yet fetched, because when bitcoin saw a new block it fetched backwards along the chain until it got to the genesis block.  Instead, they suggested people should use the term "stale block".  But the 'missing parent' usage of the term "orphan block" isn't something anything but developers were aware of because the parents always (eventually) got fetched and so users were never aware of these temporary "orphans".   Stale blocks however are common and are of some interest to users (particularly miners).   The term orphan block continued to be used to refer to stale blocks by users.  And whenever you hear someone say "orphan block" they are just referring to stale blocks.

This is especially true because the Bitcoin software was changed long ago so that 'orphan blocks' (ones where the parent isn't known) are just completely impossible:  Nodes now only fetch blocks when they're part of a header chain, and so the parents are *always* known.