The plugin could be named "audio copy-paster" or "snippet looper", but I choose to call it InstantSampler because it does what a simple 'normal' sampler does (playing audio fragments by MIDI notes), but it takes its samples (instantly) from the audio input whenever you hit a specific MIDI note for the first time. Every consecutive time you hit the same MIDI-note, it plays back the recorded fragment (or shorter, depending on the note's length).
So, is this plugin an instrument (as the name 'sampler' might suggest), or an effect? Technically, it is an effect, but one that is controlled using MIDI. But, in Logic for instance, it is considered to be an instrument, played with MIDI, while having an audio side-chain input. The bottomline is: It needs both audio - and MIDI input!