If you reach a particular rung in your career, in an organization, or in a process, you reach that level in it. I first worked with him in 1971 when we were both on the lowest rung of our careers
[ 'r&[ng] ] (noun.) 14th century. Middle English, from Old English hrung crossbar; akin to Gothic hrunga staff and perhaps to Old English hring ring; more at RING.