Indica and Sativa are both cannabis strains. Indicas are notably squatter with more crystals while Sativa is more elongated with its crystals kept in the core. Indicas are much more heavier than sativas. The high is more of a body stoned effect versus a more cerebral high from sativa. Many feel that Indica is going to make them sleepier, while Sativa gets you UP... Indicas are easier to grow, Sativas are tougher, but well worth it.
Hybrids are a little of both worlds.