Standard Definition Vs. High Definition

How does HD video differ from SD? In general, the technical parameters offer more options; this level of "customizability" is the key to the versatility of HD video across different applications, from streaming video to broadcasting, and from tape-based to digital storage. Specifically, HD video differs from SD video in four basic ways:

- aspect ratio - resolution - scanning method - frame rate

What are these parameters, and how do they affect the image?