Photographing a high contrast scene requires taking multiple exposures to make sure that information is captured in both the brightest and darkest parts of the scene. The underexposed photos capture the highlights, while the overexposed photos capture the shadows.
Photos of the same scene taken with different exposures are usually called "bracketed" photos, in reference to the Automatic Exposure Bracketing function available on many camera models.
The number of photos you need depends on the contrast in the scene, as well as the Exposure Value (EV) spacing separating the photos. If you take them in one-EV steps, you will need more photos than if you take them in two-EV steps.
For most landscapes and other types of outdoor scenes, three exposures taken in two-EV steps (i.e. -2, 0 +2 EV), or five exposures taken in one-EV steps, are sufficient.
You will need more exposures if you are photographing a scene with very high contrast, such as the interior of a room with bright windows, for instance.