This document discusses different types of compound nouns in English. It explains that noun + noun compounds are commonly used and refer to familiar things, with the first noun acting as an adjective. Some examples given are "waiting room", "police inspector", and "water bottle". It also discusses noun + 's/s + noun compounds, which are used for things loosely belonging to or related to people. Finally, it covers noun + of + noun compounds, which are used when no common compound exists, such as for units, parts, and certain fixed expressions. Some key differences in meaning between noun + of + noun and noun + noun constructions are also outlined.