What does the term 'input force' refer to in simple machines?

The term 'input force' specifically refers to the force that a user applies to a simple machine in order to perform work. This force is the initial effort needed to operate the machine, enabling it to perform a task, such as lifting an object or moving a load. This understanding of input force is critical, as it highlights the effort put into utilizing a machine to achieve an output, which is the machine's work on an object. The other options focus on other aspects of a machine's mechanics, such as total output or forces resulting from the machine's operation, which do not directly describe the input effort provided by the user.