“Adposition” is the cover term for prepositions and postpositions. Briefly, we consider an affix, word, or multiword expression to be adpositional if it:
mediates a semantically asymmetric figure--ground relation between two concepts, and
is a grammatical item that can mark an NP. We annotate tokens of these items even where they mark clauses (as a subordinator) or are intransitive.1 We also include always-intransitive grammatical items whose core meaning is spatial and highly schematic, like together, apart, and away.
Inspired by (Huddleston and Pullum, 2002), the above criteria are broad enough to include a use of a word like before whether it takes an NP complement, takes a clausal complement (traditionally considered a subordinating conjunction), or is intransitive (traditionally considered an adverb):
Even though they are not technically adpositions, we also apply adposition supersenses to possessive case marking (the clitic 's and possessive pronouns), and some uses of the infinitive marker to, as detailed in Infinitive Clauses and Genitives/Possessives.