In a speaker crossover network, the frequency point that represents the upper or lower range limits of a given speaker driver. In a two-way speaker system, the crossover frequency would be the point where the low frequency driver begins to roll off and the high frequency driver starts to cut in.
The center frequency where an audio signal is divided. The actual transition/cut-off is not usually a sharp drop off, but rather a slope such that some low frequencies (increasing in amount corresponding to frequency) are sent to the high frequency output, and some high frequencies (decreasing in amount corresponding to frequency) are sent to the low frequency output.
Frequency that is the outer limit of one of the bands of a crossover