The filter() function in Python is used to filter a sequence of elements based on a given condition and return a new sequence containing only the elements that satisfy the condition. It takes two arguments: a function that returns a Boolean value, and an iterable.

The general syntax of the filter() function is as follows:

filter(function, iterable)

Here, function is a function that takes one argument and returns a Boolean value (True or False), and iterable is the iterable being filtered.

For example, the following code uses the filter() function to filter out all the even numbers from a list:

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # Output: [2, 4, 6, 8, 10]

In this example, the lambda function lambda x: x % 2 == 0 checks whether a number is even, and the filter() function applies this function to each element in the numbers list, returning only the even numbers.

The filter() function is useful for selecting elements from an iterable that meet a certain criteria, such as selecting only the prime numbers from a list or filtering out invalid data from a dataset. It can also be used with built-in functions like bool() and str().