Gain is an increase in effective radiated power (ERP) from an antenna, usually stated in dB (deciBels). As a rule of thumb, you can multiply the radio’s output power by 4 for 6dB antennas and by 8 for 9dB antennas. A 3dB antenna gain gives an ERP of 2 times the radio’s output power. A Unity Gain antenna provides no increase in ERP.
