A more general answer...
Antennas have a number of characteristics critical to their performance, including but not limited to gain, radiation pattern, impedance, and sometimes efficiency and polarization. These performance characteristics are all tied to frequency. When designing an antenna, these characteristics can be graphed vs. frequency and there will be peaks where each characteristic is optimal and areas where they are not.
The "frequency range" of the antenna is where all of the desired characteristics are within an acceptable range. The difference between the lowest and highest acceptable frequency is called "bandwidth". When describing an antenna's range, sometimes only one of these parameters is focused on, and which one depends on the intent of use for the antenna, but ideally multiple parameters are considered.
These graphs are not necessarily simple, and there may be multiple peaks where an antenna works, and this can be designed for to get a "multi band" antenna (for instance, one that works on both 2m and 70cm), although antennas typically work at harmonic frequencies anyway.
As an example, if an antenna is designed for the amateur radio 2m band, then it would be expected that it's impedance is close to 50 ohms from 144MHz to 148Mhz so that SWR will be below (hopefully) 1.5 for the entire range. Outside of the range, the SWR may climb rapidly and become unsuitable for transmission. Reception will be attenuated as well. Also, the antenna's gain and radiation pattern will be close to what it is advertised. If this is a directional antenna, this means that it remains directional within the range; outside of the range, it may become less directional or directional in unexpected directions. For an "omnidirectional" antenna, this usually means that its angle of elevation stays low enough for good gain. Outside of the range, the elevation angle typically rises until so much energy is going up that the gain in lower angles is very low. (Gain and directionality are tied together for antennas.)