`eval()` is a built-in Python function that allows a string to be executed as Python code. It takes a string as an argument and evaluates the expression in the string as if it were a Python code. This function is often used to dynamically execute code that is created on the fly or loaded from an external source. Here is an example of how `eval()` can be used:

x = 2
y = 3
result = eval("x + y")
print(result)

In this example, the `eval()` function takes the string `"x + y"` as an argument and evaluates it as if it were a Python code. The result of the expression is stored in the variable `result` and printed to the console, which would output the value `5`. It is important to use `eval()` with caution, as it can execute any arbitrary code passed to it. Using it with untrusted input can be a security risk, as it can execute code that could cause damage to a system or reveal sensitive information.