In digital marketing, what does the term 'user engagement' primarily refer to?

User engagement primarily refers to interaction with online content because it encompasses how users respond to and participate with various forms of digital media. This can include actions such as liking, sharing, commenting, and clicking on content, which are crucial indicators of how compelling and relevant that content is to the audience.

Engagement is a key metric for assessing the effectiveness of marketing strategies, as it demonstrates a user's interest and can lead to deeper relationships with brands. The more engaged users are, the more likely they are to convert and become loyal customers.

While the other choices involve metrics related to user behavior, they do not fully encapsulate the idea of engagement. For example, time spent on a website might indicate interest but doesn't necessarily show how actively users are engaging with the content itself. Similarly, the number of web pages visited and conversion rates are important metrics but do not measure the direct interaction with content, which is at the core of user engagement.