1080p - technical definition

Refers to the 1920x1080 "progressive scan" HDTV format. Also called "Full HD" "True HD" and "Ultra HD," 1080p provides the highest resolution in the HDTV standard. However, on TV sets with screens smaller than 40", it may be difficult to distinguish the difference between 1080p and 720p, the lower of the HDTV resolutions.

1080p Out - What About 1080p In?
An HDTV set that claims 1080p resolution displays 1080p resolution, but does not necessarily accept it as input. The TV can upconvert lower-resolution signals to 1080p; however, it may not be able to accept incoming 1080p signals from high-resolution sources, such as a Blu-ray player. See progressive scan, HDTV, high-def DVD formats, 1080i and 720p.