It’s common in the South and Midwest to hear someone say something like, “I’m waiting on my Mom to come pick me up.” This is still considered incorrect in Standard American English.
To “wait on” means “to serve.” For example, “As a server, I have waited on several famous people.”
To “wait for” means to await, that is, remain in expectation of some future event, as in “I am waiting for my brother before I start making dinner.” Thus, the traditional term, “lady in waiting,” refers not to an expectant person, but to one who serves another.
If you want to be a careful speaker, try to avoid confusion here. Those who don’t know any better will not even notice if you speak correctly, but those who do know better will surely notice it if you do not!