This expression refers to somebody's talent or ability to do something quickly and well, especially something that others find difficult. For that reason, it often relates to a special or particularly clever way of doing something that requires resourcefulness as well as skill. The term is used frequently in a social and professional context, but not always in a positive sense, and shares a similar meaning to 'know-how.' Someone who 'has a knack' for something has a particular talent or skill, or an effective way of doing something. If you say 'there is a knack to it', it means there is a particular way of doing something. For example, if you have an old door in your home that is difficult to open (you might have to push the key in as well as turning the handle), you could say 'there is a knack to opening that door'. This is a casual expression used in both social and professional contexts.