Z’eir anpin literally means “small face,” and refers to the six emotions. That is, after the intellectual attributes: chochma, binah and da’as, there are six emotions until malchus. They are chessed (loving kindness), g’vura (severity, discipline, strength), tiferes (beauty, compassion, sensitivity), netzach (victory, perseverance) hod (glory, loyalty), and yesod (foundation, attraction).
The first three or higher emotions (chagas) are pure emotions and are the motivators behind the second/lower three (nehi). The lower three are more concerned with practical application and like everything that exists, the lower something exists in hishtalshelus the higher/ deeper its root. See Right, Left and Middle.