A Chorus is a device that makes the signal sound wider more harmonious, It does this by mixing the original signal with a slightly delayed or detuned signal.
It is a very simple concept but it is so effective.
This is how a simple Chorus works and below are the basic controls
Dry/Wet - Blends the original signal in with the chorused effect.
Delay - This sets the delay time between the original signal and the chorused effect signal, a long time makes the chorus more loose and short time's make it more centred and focused.
Intensity - This has 2 settings a Amount in milliseconds and a Rate/ LFO in Hertz, you look to get a sweet spot when using this as a high rate and low amount results in a nice chorus and a low rate and high amount results in thick detuning.
Feedback - This sets the amount of signal fed back into the chorus input.
The pictures below show some modern and classic emulation's plugin of chorus's used in the music industry.