Block scope refers to the visibility of variables defined within a specific block of code, such as within curly braces `{}`. In programming languages like JavaScript and Python, variables declared inside a block are only accessible within that block. This means that once you exit the block, those variables cannot be used, helping to prevent naming conflicts and unintended interactions between different parts of the code. For example, if you declare a variable inside an `if` statement or a loop, it won't be available outside of that structure. This feature promotes cleaner and more maintainable code by limiting the scope of variables to where they are needed, reducing the risk of errors.