crossover

1a. A component of an audio system that separates the audio signal into different frequency groups. Frequencies above a certain threshold or set frequency point are sent out of the device via one output while the frequencies below that point are output via a separate output (in a bi-amped, two-way system). In a tri-amped or three-way system there are two set points and three outputs.
Active crossovers are rack-mounted, either in the drive rack or amp rack, line level devices, and receive their inputs from a mixer, and output to amplifiers. The set-points are often user-adjustable so they can be tuned for various loudspeakers.

One example:

Rane AC 23S Active Crossover

1b. Passive crossovers perform the same function, but live inside the loudspeaker and split the amplified signal, directing the highs to the HF driver (tweeter) and the lows to the cone (woofer), for example.

2. A path allowing occupants of the stage to get from one side to the other without being in view of the audience. Usually upstage behind the cyc or upstage-most backdrop.

3. The shortened version of cable crossover, or cable ramp.