Precise is a Wake Word listener. Its job is to continually listen for a set wake word and activate when the sounds or speech match the wake word. Unlike other hotword detection products, Mycroft Precise is fully open source. Take a look at a comparison here.
Precise has been the default Wake Word listener for each Mycroft device since mid-March 2018. Prior to this date, PocketSphinx was the default. PocketSphinx recognizes Wake Words based on the CMU Flite dictionary of sounds.
In contrast, Precise is based on a neural network that is trained on sound patterns rather than word patterns. This reduces the dependence it has on particular languages or accents.