<span id="normalize">normalize</span>          |  A general term for converting to a more canonical form, but in the case of rustc typically refers to [associated type normalization](../traits/goals-and-clauses.md#normalizeprojection---type).
<span id="newtype">newtype</span>              |  A wrapper around some other type (e.g., `struct Foo(T)` is a "newtype" for `T`). This is commonly used in Rust to give a stronger type for indices.
<span id="niche">niche</span>                  |  Invalid bit patterns for a type _that can be used_ for layout optimizations. Some types cannot have certain bit patterns. For example, the `NonZero*` integers or the reference `&T` cannot be represented by a 0 bitstring. This means the compiler can perform layout optimizations by taking advantage of the invalid "niche value". An example application for this is the [*Discriminant elision on `Option`-like enums*](https://rust-lang.github.io/unsafe-code-guidelines/layout/enums.html#discriminant-elision-on-option-like-enums), which allows using a type's niche as the ["tag"](#tag) for an `enum` without requiring a separate field.
<span id="nll">NLL</span>                      |  Short for [non-lexical lifetimes](../borrow_check/region_inference.md), this is an extension to Rust's borrowing system to make it be based on the control-flow graph.
<span id="node-id">node-id or `NodeId`</span>  |  An index identifying a particular node in the AST or HIR; gradually being phased out and replaced with `HirId`. See [the HIR chapter for more](../hir.md#identifiers-in-the-hir).
<span id="obligation">obligation</span>        |  Something that must be proven by the trait system. ([see more](../traits/resolution.md))
<span id="placeholder">placeholder</span>      |  **NOTE: skolemization is deprecated by placeholder** a way of handling subtyping around "for-all" types (e.g., `for<'a> fn(&'a u32)`) as well as solving higher-ranked trait bounds (e.g., `for<'a> T: Trait<'a>`). See [the chapter on placeholder and universes](../borrow_check/region_inference/placeholders_and_universes.md) for more details.
<span id="point">point</span>                  |  Used in the NLL analysis to refer to some particular location in the MIR; typically used to refer to a node in the control-flow graph.
<span id="projection">projection</span>        |  A general term for a "relative path", e.g. `x.f` is a "field projection", and `T::Item` is an ["associated type projection"](../traits/goals-and-clauses.md#trait-ref).
<span id="pc">promoted constants</span>        |  Constants extracted from a function and lifted to static scope; see [this section](../mir/index.md#promoted) for more details.
<span id="provider">provider</span>            |  The function that executes a query. ([see more](../query.md))
<span id="quantified">quantified</span>        |  In math or logic, existential and universal quantification are used to ask questions like "is there any type T for which is true?" or "is this true for all types T?"; see [the background chapter for more](./background.md#quantified).
<span id="query">query</span>                  |  A sub-computation during compilation. Query results can be cached in the current session or to disk for incremental compilation. ([see more](../query.md))
<span id="recovery">recovery</span>            |  Recovery refers to handling invalid syntax during parsing (e.g. a missing comma) and continuing to parse the AST. This avoid showing spurious errors to the user (e.g. showing 'missing field' errors when the struct definition contains errors).
<span id="region">region</span>                |  Another term for "lifetime" often used in the literature and in the borrow checker.
<span id="rib">rib</span>                      |  A data structure in the name resolver that keeps track of a single scope for names. ([see more](../name-resolution.md))
<span id="rpit">RPIT</span>                    |  A return-position `impl Trait`. ([see the reference](https://doc.rust-lang.org/reference/types/impl-trait.html#abstract-return-types)).