The word "knack" refers to a skill or ability that comes naturally and easily to someone, often without formal training. It is an innate talent or aptitude for doing something well, typically involving a specific activity or task. The term can also refer to a clever way of achieving a particular result, or an ability to learn quickly how to do something new. In essence, "knack" describes the ability to perform a certain action with ease and expertise due to natural talent or acquired skill.