A `staffer` is a person employed by an organization — a member of its staff. The word is American in origin and still feels American, and it belongs above all to two worlds: politics and the news. A congressional staffer is one of the people who work in a politician's office, writing speeches, answering letters, doing research. A staffer at a magazine is a writer on the payroll, as opposed to a freelancer who is paid per article. You meet the word constantly in news reporting: "a White House staffer said…", "junior staffers were told to stay late".

It is neutral in feeling but slightly journalistic — it is the word a reporter uses more than the word a company uses about itself. A staffer is usually not the boss; the word quietly suggests someone doing the work rather than making the decisions, which is why "senior staffer" needs the word "senior" to lift them. In British English people more often say "member of staff" or "staff member", though `staffer` has been spreading. Note that `staff` on its own is already a group word — "the staff are meeting" — so `staffer` fills a real gap: it gives you a way to talk about ONE of them.