[doc] Revise the glossary documentation (#6205)

### What changes were proposed in this pull request?

This PR fixes the glossary docs.

### Why are the changes needed?

The glossary is reordered for quick reference.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

N/A

Co-authored-by: Qiming Teng <[email protected]>