Both the iPad and the iPad 2 have an IPS display with a screen resolution of 1024x768. This is close to the screen resolution of the iPhone 4's Retina Display, which is 960x640, but the iPad has a display measured at 9.7 inches diagonally compared to the iPhone 4's 3.5 inches, which gives the iPhone 4's display 326 pixels per inch compared to the iPad's 132 pixels per inch.
What is an IPS display?
In-plane switching (IPS) gives the iPad a larger viewing angle. Some laptops have a reduced viewing angle, which means the screen becomes difficult to see when standing to the side of the laptop. The IPS display means more people can crowd around the iPad and still get a clear look at the screen.