add scope, mongodb and sql-injection

glossary/MongoDB.md

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+### MongoDB
+
+MongoDB stores data in flexible, JSON-like documents, meaning fields can vary from document to document and data structure can be changed over time

glossary/SQL-injection.md

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+### SQL injection
+
+SQL injection is a code injection technique, used to attack data-driven applications.

glossary/Scope.md

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+### Scope
+
+Each function has its own scope, and any variable declared within that function is only accessible from that function and any nested functions.