1. In "anime" (Japanese animation) fan circles, when you say something is "ecchi" you mean it is erotic, but usually not with all-out sex or anything very vulgar. Basically like "hentai" but more softcore.
2. In Japanese: comes from English letter "H," possibly an abbreviation of the word "hentai" which means perverted/sexually deviant. Refers to the act of sex, or can refer to anything sexual in nature if used as an adjective with the -na suffix.
1. This anime has some ecchi parts, but nothing too bad--just a panty shot and a part where you see a girl's nipple for a few seconds.
2. Ecchi shiyou. ("Let's have sex.")