The `filter()` function is a built-in method in programming languages like Python that allows you to create a new iterable by selecting elements from an existing iterable based on a specified condition. It takes two arguments: a function that defines the filtering condition and the iterable to be filtered. Only the elements that return `True` from the function are included in the new iterable. For example, if you have a list of numbers and want to keep only the even ones, you can use `filter()` with a function that checks if a number is even. This makes it a powerful tool for data processing and manipulation, helping to streamline tasks by focusing on relevant data.