1. In an antenna, the range of frequencies within which its performance, in respect to some characteristic, conforms to a specified standard.
2. In a wave, the least frequency interval outside of which the power spectrum of a time-varying quantity is everywhere less than some specified fraction of its value at a reference frequency.
3. The number of cycles per second between the limits of a frequency band.
Sense 2 permits the spectrum to be less than the specified fraction within the interval. Unless otherwise stated, the reference frequency is that at which the spectrum has its maximum value.
4. In information theory, the information-carrying capacity of a communications channel.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use