diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 7f07e4fddef..1cedd6eedfa 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -370,7 +370,7 @@ pub enum ErrorKind {
 
     // "Unusual" error kinds which do not correspond simply to (sets
     // of) OS error codes, should be added just above this comment.
-    // `Other` and `Uncategorised` should remain at the end:
+    // `Other` and `Uncategorized` should remain at the end:
     //
     /// A custom error that does not fall under any other I/O error kind.
     ///
@@ -882,6 +882,13 @@ impl Error {
 
     /// Returns the corresponding [`ErrorKind`] for this error.
     ///
+    /// This may be a value set by Rust code constructing custom `io::Error`s,
+    /// or if this `io::Error` was sourced from the operating system,
+    /// it will be a value inferred from the system's error encoding.
+    /// See [`last_os_error`] for more details.
+    ///
+    /// [`last_os_error`]: Error::last_os_error
+    ///
     /// # Examples
     ///
     /// ```
@@ -892,7 +899,8 @@ impl Error {
     /// }
     ///
     /// fn main() {
-    ///     // Will print "Uncategorized".
+    ///     // As no error has (visibly) occurred, this may print anything!
+    ///     // It likely prints a placeholder for unidentified (non-)errors.
     ///     print_error(Error::last_os_error());
     ///     // Will print "AddrInUse".
     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));