A flashgun is the piece of camera equipment that fires a very bright burst of light when you take a photograph, so the picture is not dark. Older ones had a handle and sat beside the camera, a little like a gun, which is why the name has gun in it. There is no bullet; it is not a weapon. Photographers, especially in British English, still say flashgun for a separate flash you hold or clip on. Most people with a phone just say flash. Neutral, a bit technical. Though actually, the tiny light on the front of a phone is doing a similar job, but people almost never call that a flashgun.

閃光燈（尤其指外接、手持的那種；口語多說閃燈）