What does 1920 x 1080 pixel resolution mean in terms of 720p, 1080i, etc?

Answer 1

720p is 1280x720, so the TV will scale the signal up to fit the screen (1080 lines)
1080i , signal is 1280x540, so the TV will combine two x540 fields to create a 1080 picture
1080p signal. This is native for the TV, no scaling.
Standard definition: Input will be scaled to 1080 lines