diff --git a/glossary/Event-loop.md b/glossary/Event-loop.md
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+### Event loop
+
+The event loop handles all asynchronous callbacks. 
+Callbacks are queued in a loop, while other code runs, and will run one by one when the response for each one has been received.
+The event loop allows JavaScript to perform non-blocking I/O operations, despite the fact that JavaScript is single-threaded.
diff --git a/glossary/HTTP-and-HTTPS.md b/glossary/HTTP-and-HTTPS.md
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+### HTTP and HTTPS
+
+The HyperText Transfer Protocol (HTTP) is the underlying network protocol that enables transfer of hypermedia documents on the Web, usually between a client and a server.
+The HyperText Transfer Protocol Secure (HTTPS) is an encrypted version of the HTTP protocol, that uses SSL to encrypt all data transfered between a client and a server.
diff --git a/glossary/Regular-expressions.md b/glossary/Regular-expressions.md
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+### Regular expressions
+
+Regular expressions (known as regex or regexp) are patterns used to match character combinations in strings.
+JavaScript provides a regular expression implementation through the `RegExp` object.
diff --git a/glossary/String.md b/glossary/String.md
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+### String
+
+Strings are one of the primitive data types in JavaScript.
+They are sequences of characters and are used to represent text.
diff --git a/glossary/Value-vs-reference.md b/glossary/Value-vs-reference.md
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+### Value vs reference
+
+When passing a variable by value, a copy of the variable is made, meaning that any changes made to the contents of the variable will not be reflected in the original variable.
+When passing a variable by reference, the memory address of the actual variable is passed to the function or variable, meaning that modifying the variable's contents will be reflected in the original variable.
+In JavaScript primitive data types are passed by value while objects are passed by reference.