A tiff is a minor, relatively unimportant argument or fight. A tiff with your brother might start over the subject of whose turn it is to take out the trash.
It's no fun to have a tiff with someone, but it's usually resolved or forgotten easily. When you have a tiff with a friend, it's inevitably a squabble over some silly topic, and if you bicker with your boyfriend, you can call it a "lovers' tiff." In the 1700s, a tiff was an "outburst of temper," from an unknown source. Some word experts suggest the word echoes the sound of a "puff of air or gas."