Capa­cit­ive touch sens­ing used for stuff like touch-react­ive tab­lets and phones, as well as con­trol pan­els for appli­ances (which is where you may have used it before). This HAT allows you to cre­ate elec­tron­ics that can react to human touch, with up to 12 indi­vidu­al sensors.

The main dif­fer­ence between this and some­thing like the Makey Makey board is that there is no need for a ground wire.