Over the last decades, the Internet and mobile technology have consolidated the digital as a public sphere of life. Designers are asked to create engaging digital experiences. However, in some cases engagement is seen as a psychological state, while in others it emphasizes a participative vein. In this paper, I review and discuss both and propose a new definition to clarify the concept engagement with computers. Thus, engagement is a quality of an active connection between a user and a computing product, either a website or a mobile phone app. Studying it requires understanding a set of aspects like the user's affect, motivation and attention, as well as the product's design, content and composition. Finally, I propose explaining these concepts aligned with engagement and integrate them into a preliminary model to measure the manifestations.