For mine, it has always meant, "I'm getting close to laying an egg."
Possibly, "I'm getting close to laying an egg so get out of the way" since it is nearly always done when her preferred nest is already in use. For the first few days of their laying when they were pullets just beginning to lay it was also done when the nests were empty.
I have a coop/run combo so they never wait to go in or out. So I wouldn't know if it also means "get out of my way" separate from needing to lay an egg.