Constant panty shots, bouncing breasts and dubious camera angles are hallmarks of an Ecchi title. These titles are usually sexualized and designed to titillate, depicting perverted themes and focusing heavily on the female body. Nosebleeds, suspicious hand positions, faceplanting into bosoms, expressive and exaggerated body parts and other tropes characterize this genre.
A harem includes three or more characters who potentially show romantic interest in a male protagonist. The sex, gender, or orientation of the harem members is irrelevant as long as they exclusively, or at least primarily, are vying for the affections of the same individual - who may or may not reciprocate towards one, several, or none of these romantic rivals.
Yuri is a genre that depicts homosexual relationships between women. Japan typically uses this single category for all forms of these relationships, sexual or not. In the West, the term Shoujo-ai categorizes stories that focus on the emotional aspects of the relationships, while Yuri categorizes more of the sexual aspects and explicit content. As Anime-Planet's audience is mostly based in the West, we use the Western definition for both Yuri and Shoujo-ai.