Let's start with this, from the Wikipedia article on insect morphology: "Antennae vary greatly among insects, but all follow a basic plan, the first and second true segments of which are termed the scape and pedicel, respectively. The remaining antennal segments or [more properly called] flagellomeres are jointly called the flagellum."
The difference between the two true segments and the antennal appendage called the flagellum is the segments have muscles, while the flagellum lacks muscles, and its movements are controlled by the motion of the pedicel and by changes in hydrostatic pressure.
A bit of confusion for ants is that we may refer to the parts of the antenna as the scape and the funiculus, which is the pedicel + the flagellum, because the antennal pedicel often has a similar appearance to the flagellomeres, or the parts of the flagellum. And for convenience, we count the scape, pedicel and flagellomeres each as individual "segments", even though this is not technically correct. The most common numbers of these "segments", and the count thought to have occurred in the ancestor of ants, and related bees and wasps, is 12 in females and 13 in males. In many ants, especially small and subterranean kinds, the numbers are reduced, but the general rule is that male antennae have a relatively shorter scape, and have one (or a few) more "segment" (flagellomere) than the females of the same species.