露点 (dew point / lùdiǎn) is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into liquid water.
Why it is blocked: Certainly not for its scientific meaning. An alternative meaning for 露 is “reveal” or “expose.” 点 can not only mean “point” but also “a little.” Thus, slang for “reveal a bit (of skin)”, or translated more loosely into English, something like “nipple slip" or "crotch shot.” Based on news references and Google searches (NSFW), the term can be used both for accidental cases and intentional exposures (eg risque photo shoots). But though the latter may be titillating, its generally non-nude. [Status - 2/9/12: blocked]
Note: A similar word, 暴露 (expose, reveal, or unbare / bàolù) is used in the same way as ludian. A noun form, 暴露癖 (bàolùpǐ), is equivalent to exhibitionism or flashing. This is also blocked. [Status - 1/6/12: blocked; 2/5/12: unblocked]