Lenses with focal lengths greater than 35mm are telephoto lenses. They allow you to take close-up photos without getting closer to your subject.
Unfortunately, choosing lenses for a digital SLR is more complicated. That's because the sensor that captures images is usually smaller than a frame of 35mm film. Lenses, on the other hand, are still labeled for 35mm film cameras. That is, unless you buy a digital-specific lens.
Because digital sensors are smaller than film frames, images are magnified. This is called field of view crop. There are full-frame SLRs; these have sensors the same size as a 35mm frame of film. They do not suffer from field of view crop. But, their high prices put them out of range of most buyers.
Field of view crop is also called the focal length multiplier or multiplication factor. Common values for field of view crop range from 1.3 to 2. You multiply a lens' focal length by the multiplier to determine its 35mm equivalent.