From the free dictionary
high-res·o·lu·tion (hrz-lshn)
adj.
1. Relating to an image that has fine detail.
2.
a. Of or relating to an output device that produces images that contain a large number of dots per unit of area and are therefore sharp and detailed.
b. Of or relating to a raster-based image that contains a large number of pixels per unit of area.
Exactly HOW high a resolution sort of depends on the original capture device - an old 5mb camera has a max resolution less than a new 15mb camera. But both can produce sharp and detailed images, the only difference is the maximum print size that can be obtained before the image loses clarity.
Set your camera to the largest file size its capable of (L) or whatever, and to the best quality (High) and you're set to go.