Cannabis Sativa varieties are differentiated and named by their overall appearance, aroma (terpene profile) & cannabinoid content. This allows us to distinguish them from each other easily & eventually will allow us to realize the medicinal differences between varieties.
Terpenes are hydroxy (hydrogen & oxygen) molecules that give off aromas & assist cannabinoids in their functions. There are over 200 terpenes that can be found in Cannabis Sativa in various amounts. A-Pinene is a common terpene that smells of pine trees or slightly woody & assists in memory retention, is a bronchodilator, & provides uplifting effects.
Terpenoids are terpenes that have been in contact with oxygen, usually through the curing process, and have degraded to a certain point. Terpenes/terpenoids are nature's way to repelling certain insects while attracting beneficial insects/animals.
Trichomes are the small resin glands that contain a large amount of cannabinoids & terpenes. They can vary in color slightly, but can be mostly clear or milky depending on genetics & environmental factors.
Resin is a thicker-than-sap liquid made within the outer layers of most plants. Its function is to excrete from "wounds" in plants to cover and protect the wound from infection. Resin contains many compounds for helping in recovery for the plant that also benefits animals when consumed.