Concept: adposition

Definition

An adposition is a °flag that is not an °affix.

Comments

That adpositions and case affixes are functionally similar has long been recognized, but it was only after Haspelmath (2005) that the term "flag" (which was coined in the 1980s) gained ground

Croft's comparative concept
adposition (STR):

adposition (STR) = a flag which occurs as an independent word, in contrast to a case affix. Adpositions are distinguished by position: preposition, postposition, and circumposition. (Section 4.3)

Wikipedia
adposition
SIL Glossary
adposition
Quotation
"Adpositions ... may be defined as grammatical tools which mark the relationship between two parts of a sentence: one is the element which an adposition governs. It is traditionally called its complement and is mostly represented by a noun or noun-like word or phrase. It will be called here the governed term. The other part is an entity which either functions as the predicate of this sentence, or is a non-predicative noun. Adpositions mark, therefore, the fact that, from the syntactic point of view, their governed term depends on a head." (Hagège 2010: 1)
Sources
Haspelmath 2005; Hagège 2010