The term "tier" has multiple meanings depending on its context.
In a general sense, it can refer to any level or layer within a system or structure. For example, in computer networking, tiers are used to describe different levels of access and security for users. In this case, the word is often used as a noun.
However, "tier" can also be used as a verb meaning to arrange things in layers or groups according to importance or quality. For example, one might say they need to "tier" their priorities when managing multiple tasks at once. In this case, the word is often used as a transitive verb.
Overall, the term "tier" can be used both as a noun and a verb depending on its context within a sentence or conversation.