Indica and Sativa are the two generic categorizations of cannabis most commonly used today. I say "generic categorizations" versus "species", because scientists haven't yet proven that Indica and Sativa plants are truly genetically distinct! For now, Indica and Sativa can be distinguished by the history of their cultivation, their physical structure, and the type of high most commonly associated with each.
Sativa, on the other hand, refers to cannabis strains originally cultivated in various equatorial and tropical climes throughout the globe -- places like Central America and various parts of Africa or Southeast Asia. Sativa plants are typically tall, slender, and sport wider, fan-like leaves. Sativas were traditionally cultivated strictly for the medical and recreational effects of direct cannabis use, and they typically produce an elevated "mind high" without the "couch lock". For this reason, Sativa is commonly considered the day-time or "active" user's cannabis. There is one thing to note about Sativas though: they produce loose, flighty states of mind where panic attacks and paranoia are more likely.
For these reasons, you might see strains labeled like so:
Indica/Sativa
60/40
This label gives the genealogy of the cannabis in a way that also reveals the type of high users will likely experience.
A strain labeled like the example above will generally give a nice, comprehensive, tingly stone that won't force a nap. The more common hybrids are typically like the above example -- Indica heavy.
I (Jeff) personally prefer the opposite, more like:
Indica/Sativa
20/80
This Sativa heavy hybridization usually produces pleasant, active, creative states of mind without the potential for panic, and the small dose of Indica adds a nice warmth that may go lacking in pure Sativas.So, now you can shop with a better idea of what you actually want out of your purchase.