Crystal Habit.
The characteristic shape a mineral takes when it grows freely, such as prismatic, tabular, cubic, or massive.
Crystal habit is the word mineralogists use for the typical shape a mineral grows into when nothing crowds it. Each species has a preferred internal arrangement of atoms, and when a crystal forms with enough room, that arrangement shows itself on the outside as a recognisable form.
Quartz, for instance, has a prismatic habit: long six-sided columns ending in pyramidal points. Pyrite favours a cubic habit, which is why it so often appears as the small brassy cubes found in school collections. Garnet often grows as a dodecahedron (twelve-faced ball). Selenite is tabular or bladed. Mica grows in sheets. When a crystal is too crammed in to express its preferred form it is called massive, which is the word for, say, most rose quartz boulders or a chunk of jade.
For buyers, habit is a useful identification clue and an aesthetic consideration. A natural quartz point looks the way it does because the mineral grew that way, not because it was carved. Recognising habit is the first step in telling natural specimens from cut and polished pieces, and from glass or resin imitations.