A chorus effect is a type of effect that adds depth, width, and harmonic presence to a sound. It is most commonly used on vocals, synths and electric guitars and electric pianos and very rarely to bass instruments.
A chorus effect is a type of audio device or software that in a couple of words modifies the an audio signal in the way below:
It creates one or more copies of the input signal modulates its pitch(es) subtly in time and then blending all of them with the original signal.
The resulting sound is usually described as similar to the sound of multiple voices or instruments playing simultaneously. Think it like 2 or more guitarists playing the same riff silmutaneously - they could never have exactly the same performance, there will be some small variations but the sound will for sure sound fuller that if only one was playing.
So, it is a good way to create depth, depth that is not achievable by the playing of one instrument and thickness in the stereo field.
Hornet Plugins Chorus 60
Almost every software synth has its dedicated chorus device - Omnisphere, Diva, Pigments to name a few.
Most of the times I use chorus in a synth patch when I need to add more dimension to the sound and make it richer in feeling. My main preference is to keep the rate of the LFO very low and the depth very high but this is not a rule of course. Experimenting with those settings - as well as some additional features that some chorus plugins offer, like Width which determines how much will the output signal will be spread in the stereo field- give a variety of interesting results.
The same goes when I use chorus for electric guitar - I find that in melodic lines it makes the sound more liquid in a pleasant way, but also we could use chorus for a variety of applications when it comes for guitar.
For a lot of our soundbanks and synth patches I either use an amount of chorus or even assign a macro to the chorus' wet/dry knob. I find Chorus a very special and useable audio effect and maybe it is the modulation type of effect I mostly use in my sound design process and in my productions.
There are plenty hardware like guitar pedals or even included in multieffect units and software choruses today with very high quality. Most of the DAWs (if not every one) have a stock Chorus effect plugin. We could find either digital clean choruses or some emulations of hardware unit with a bit of coloration in sound. The most iconic hardware with a lot of digital emulations today I think is the chorus effect that was part of the classic JUNO synths manufactured by Roland.