A dipole is an antenna. It is a fundamental form of antenna consisting of a single wire whose length is approximately equal to half the transmitting wavelength.
The length of a half wave in space is approximately:
length (metres) = 150 / Freq (Mhz) or length (feet) = 492 / Freq (Mhz).
The actual physical length in practice is slightly different from this owing to other factors.
A most popular dipole known to almost everyone is the folded dipole which forms part of most V.H.F. T.V. Antennas.