diff --git a/glossary/CSS.md b/glossary/CSS.md
new file mode 100644
index 000000000..4e21c2f11
--- /dev/null
+++ b/glossary/CSS.md
@@ -0,0 +1,4 @@
+### CSS
+
+HTML stands for Cascading Style Sheets and is a language used to style web pages.
+CSS documents are plaintext documents structured with rules, which consist of element selectors and property-value pairs that apply the styles to the specified selectors.
diff --git a/glossary/keyword_database b/glossary/keyword_database
index 075ceef0e..50e863af6 100644
--- a/glossary/keyword_database
+++ b/glossary/keyword_database
@@ -5,6 +5,7 @@ callback
 class
 constant
 cross-site-scripting-xss
+css
 currying
 dns
 dom