A more thorough explanation:

A means-plus-function clause is a part of a patent claim that asserts that the design is a way to perform a given function or is a step in the process of performing a given function. This clause will be interpreted as including the structure or means stated in the patent specification and equivalents at the time of interpretation or infringement, but not all possible means of achieving the same function.

For example, a patent for a device that dispenses medication may include a means-plus-function clause that describes the mechanism for releasing the medication. The clause would be interpreted to include the specific mechanism described in the patent and any equivalent mechanisms that perform the same function.