informal content within section 4.4 Terms and Definitions

[michaelficarra]

Terms and Definitions contains a lot of informal prose. We typically use full sentences, include all necessary context, use capitalisation and periods, etc. This section deviates from that. We should improve it.

Relatedly, once this prose is cleaned up, we may want to move each definition from this section to a more appropriate section. See #1278.

[jmdyck]

(The lack of full sentences, context, capitalization, and periods isn't "informality" per se, it's ISO definition style, in which the defining text should be a drop-in replacement for the term being defined.)