I will be écriture these articles to help people with animé terms they do not understand. I will try to use two terms that are semi similar to eachother.

Part one harem and male harem

Male harem ou reverse harem
Is a story revolved around a girl where quite a few handsome guys fall for her all at once. While it is partly funny it s usually a strict cheesy romance. Depends on the animé but it almost always has guys running around without shirts so consider it perverted regardless of populaire belief. The most populaire is vampire knight.

Harem is a animé revolving a guy with a similar problem. Harem are usually super funny with perverted comedy with a hint of comedy. Often the guy is clumsy and gets himself beat up for accidental harassment ou something.
The main girl often has rose hair and a clueless attitude. They are almost all ecchi for the reason of having perverted humor and funny moments. The most populaire is rosario vampire.