Paizuri

[Tina]

Breast fucking. (Japanese)

[Justin Bieber]

Paizuri is a subcategory of hentai that involves breast sex, also known in America and other parts of the world (slang) as titty fucking, tit fucking, etc.
When Paizuri first became a big thing in hentai, it was most commonplace for the character giving paizuri to the second party to have large or huge breasts. However, in the past few years or so, this has become more varied. In many types of hentai, women of all breast sizes can give paizuri.
Some varieties: Double paizuri (involving two women performing it on a single penis), multi paizuri (same as double but involving more women), clothed paizuri, futa (she-male) paizuri, etc...

[Jessica]

In essence, breast sex. It is a Japanese word, but is used commonly by Otakus that are total perverts and actually looked up the Japanese word for tit fucking.