Name for words like whatchamacallit, doohickey, thingamabob [duplicate]

Is there a name for words like whatchamacallit, doohickey, thingamabob, doodad, thingamajig, whatsit, etc.?

Somehow it seems like there should be a word to describe the general term for a word that you use for referring to something when you cannot remember what it is called.

(Computing names like foo, bar, baz are examples of metasyntactic variables but those are a slightly different category.)

These are placeholders:

A placeholder is a word (such as whatchamacallit) used by speakers to signal that they don't know or can't remember a more precise word for something. Also known as a kadigan, tongue-tipper, and dummy noun.
_ThoughtCo.