From a user point of view, kind of like effects pedals[0], but inside your computer, and not necessarily guitar-oriented. From the computer's point of view, a

From a user point of view, kind of like effects pedals[0], but inside your computer, and not necessarily guitar-oriented. From the computer's point of view, a host program (probably a DAW) feeds an audio stream to a plugin, eg. 512 samples at a time, the plugin does whatever and sends back 512 samples, which the DAW may optionally route to another plugin and so on. Plugins are routed by software, instead of the 1/4" jack cables used by most hardware effects pedals. Modern audio production often uses a lot of these effects / plugins, like dozens or hundreds across a multi-track project, then a bunch more once the tracks are mixed together. Each plugin can either affect the sound very subtly, or make it completely unrecognizable, or something in the middle. Contains some omissions and half-truths, but that's kind of the gist of it. [0] https://www.youtube.com/watch?v=t7nj1d-P9-I https://www.youtube.com/watch?v=t7nj1d-P9-I