The `eval()` function is a built-in function in programming languages like JavaScript and Python that evaluates a string as code. When you pass a string containing valid code to `eval()`, it executes that code within the current scope, allowing for dynamic code execution. This can be useful for tasks like parsing user input or generating code on the fly. However, using `eval()` can pose security risks, especially if the input is not properly sanitized. It can execute arbitrary code, which may lead to vulnerabilities such as code injection. Therefore, it's generally recommended to avoid using `eval()` unless absolutely necessary and to consider safer alternatives.