diff --git a/Glossary.md b/Glossary.md
index b5e8908e2a..0c90ff05e9 100644
--- a/Glossary.md
+++ b/Glossary.md
@@ -401,6 +401,14 @@ Related definitions in the compiler:
 - old compiler: search "pub enum Content" in [types/src/subs.rs](crates/compiler/types/src/subs.rs)
 - new compiler: search "pub const Content" in [check/canonicalize/CIR.zig](src/check/canonicalize/CIR.zig)
 
+## Flat Type
+
+Represents types without indirection, it's the concrete form that types take after
+resolving [variables](#type-variable) and [aliases](#type-alias).
+
+definitions in the compiler:
+- old compiler: search "pub enum FlatType" in [types/src/subs.rs](crates/compiler/types/src/subs.rs)
+- new compiler: search "pub const FlatType" in [types/types.zig](src/types/types.zig)
 
 ## Canonicalization
 
diff --git a/src/types/types.zig b/src/types/types.zig
index 03277f24d9..342228275c 100644
--- a/src/types/types.zig
+++ b/src/types/types.zig
@@ -208,7 +208,8 @@ pub const TypeIdent = struct {
 
 // flat types //
 
-/// A "flat" data type
+/// Represents type without indirection, it's the concrete form that a type
+/// takes after resolving type variables and aliases.
 pub const FlatType = union(enum) {
     str,
     box: Var,