There is a problem some photographers have with their camera: focus does not seem to be on the right (expected) point. In other words some parts of the picture that should be in focus are out of focus. This could be due to several things: back focus, front focus, due to the lens, the camera or both. The easiest way to determine if your equipment has a problem, or that it is just about your technique, some people have developed a detailed procedure to analyze the issue.
Here is the most popular focus chart being used for such a test:
http://www.focustestchart.com/chart.html
A bit off topic, all kinds of test charts can be found here:
http://www.northlight-images.co.uk/article_pages/test_images.html
They include charts to test lens resolution, colors,...