What is the difference between 1080i and 1080p signals?

Television images are made of horizontal lines. 1080 indicates that the image is a high definition one and uses 1080 lines to create the image. The "i" and "p" define how the lines will be delivered.
"i" stands for interlaced. An interlaced picture will start by showing all the odd numbered lines from 1, 3, 5 etc to line 1079. Then, starting at the top of the screen, all the even numbered lines will be shown from 2 to 1080. so in two passes from the top to the bottom, every line will be shown. the passes each happen 50 or 60 times each second so a full frame will be shown 25 or 30 times each second.

"p" stands for progressive. A progressive scan starts at the top of the screen and shows each line in order from line 1 to line 1080. A single pass is all that is needed to build a full image. That means that a full frame will be delivered 50 or 60 times each second. It is easy to see that a progressive signal displays lines at twice the rate of an interlaced signal. It therefore needs to send twice as much data as an interlaced signal.

Broadcasters do not transmit 1080p at the moment and are unlikely to do so for at least a few years. The standard broadcast HD signals are 1080i (and 720p). Most HD televisions will handle 1080p signals but they are found only on local sources such as Bluray, games consoles and computers.

In practical terms, the difference between "i" and "p" is that progressive signals show smoother movement compared to interlaced. For most programs, the difference is not obvious so the lack of a 1080p signal from broadcasters is not a big deal.

A final note on the frame rates: North America uses a 60Hz rate as standard while Europe uses 50Hz. The reason is a historical one but the frame rates will not be changing for either region any time soon.
Television images are made of horizontal lines. 1080 indicates that the image is a high definition one and uses 1080 lines to create the image. The "i" and "p" define how the lines will be delivered.
"i" stands for interlaced. An interlaced picture will start by showing all the odd numbered lines from 1, 3, 5 etc to line 1079. Then, starting at the top of the screen, all the even numbered lines will be shown from 2 to 1080. so in two passes from the top to the bottom, every line will be shown. the passes each happen 50 or 60 times each second so a full frame will be shown 25 or 30 times each second.

"p" stands for progressive. A progressive scan starts at the top of the screen and shows each line in order from line 1 to line 1080. A single pass is all that is needed to build a full image. That means that a full frame will be delivered 50 or 60 times each second. It is easy to see that a progressive signal displays lines at twice the rate of an interlaced signal. It therefore needs to send twice as much data as an interlaced signal.

Broadcasters do not transmit 1080p at the moment and are unlikely to do so for at least a few years. The standard broadcast HD signals are 1080i (and 720p). Most HD televisions will handle 1080p signals but they are found only on local sources such as Bluray, games consoles and computers.

In practical terms, the difference between "i" and "p" is that progressive signals show smoother movement compared to interlaced. For most programs, the difference is not obvious so the lack of a 1080p signal from broadcasters is not a big deal.

A final note on the frame rates: North America uses a 60Hz rate as standard while Europe uses 50Hz. The reason is a historical one but the frame rates will not be changing for either region any time soon.