How can I tell if an antenna is a dipole antenna
The term dipole comes from the fact, that such an antenna has two poles instead of one (monopole). 

A monopole looks like a simple pole standing on the ground, which is the reference (other pole) in that case. 

In a dipole, you have two poles (often pointing in different directions) referencing each other and no ground plane. 

Because of that, a dipole has to be fed with a symmetrical signal, whereas a monopole can be fed with a asymmetrical signal (referenced to ground).