Questions about example sentences with, and the definition and usage of "Yammer"

A: "yammer" means to talk a lot, or a person who talks a lot. Together, it means "you're the talker, I'm the muscle (- the one that does the physical work)"

A: talking a lot, being repetitive and annoying

A: I don't hear the word "yammer" very much, but it's not childish. It's pretty much always used negatively.

Some sentences might be:

"My brother yammered on and on about his game."

"The customer continued to yammer about his problems."

"They kept yammering on, even though no one was listening."

A: it's used in everyday speech, yes.