Deskew
From The Glossary of Digital Photography
When an image is skewed, its horizon, or a vertical line, is not straight. Deskewing brings the image back to a straight format. An image may be skewed because it was not straight when the original was scanned, or it may be due to the camera being tilted when the image was created. , To deskew an image in Photoshop, use the ruler tool to draw a line—either horizontal or vertical— and then use the rotate - arbitrary command to rotate the image until it is straight.
