What type of spyware silently captures and stores each keystroke that a user types on the computer's keyboard?

The correct answer to the following question will be "Key logger".

Explanation:

Key loggers are a type of spyware, where clients are incapable of recording their actions. They could be used for a wide range of applications; hackers can using them to manipulate the personal information purposefully, and employees can are using them to track workplace practices. It can secretly record and store any keystroke a client inputs on the keyboard on the machine.

Therefore, Key logger is the right answer.