Indoor cannabis strains are, in the Northern hemisphere, generally only intended for growing indoors with artificial light. The optimal light conditions available indoors will allow these strains to reach their full potential.
Outdoor cannabis strains are those that may be grown outside during spring and summer. Their hardiness and early-flowering tendencies will allow them to ripen even in a short, cool summer.
Greenhouse strains are suitable for the widest range of growing conditions. Greenhouse cannabis seeds may be grown indoors with artificial lights just as successfully as the regular indoor strains, but they can also be grown in a greenhouse with just the power of the sun.