diff --git a/glossary/Selector.md b/glossary/Selector.md
new file mode 100644
index 000000000..d8b644a2d
--- /dev/null
+++ b/glossary/Selector.md
@@ -0,0 +1,4 @@
+### Selector
+
+A CSS selector is a pattern that is used to select and/or style one or more elements in a document, based on certain rules.
+The order in which CSS selectors apply styles to elements is based on the rules of CSS specificity.
diff --git a/glossary/array.md b/glossary/array.md
index 22a89fc5d..068e0b383 100644
--- a/glossary/array.md
+++ b/glossary/array.md
@@ -1,4 +1,4 @@
-### array
+### Array
 
 Arrays are used to store multiple values in a single variable.
 Arrays are ordered and each item in an array has a numeric index associated with it.
diff --git a/glossary/callback.md b/glossary/callback.md
index ac843d2b7..2d5c041e9 100644
--- a/glossary/callback.md
+++ b/glossary/callback.md
@@ -1,4 +1,4 @@
-### callback
+### Callback
 
 A callback function, also known as a high-order function, is a function that is passed into another function as an argument, which is then executed inside the outer function.
 Callbacks can be synchronous or asynchronous.