[LeBlanc]

The definition of engagement should depend on the application.

Measuring engagement as daily users / monthly users may make sense for Facebook. However, for a company like WePay, engagement should be measured as the number of users who are actually taking action that involves a monetary transaction, because that is what makes the company money (and this is the engagement metric that the article states WePay is using).

[far33d]

Engagement should be a relative metric: so in this case, maybe, the % of users who sign up that make a transaction in a time period. Otherwise it's not really meaningful without other data (ad spend, total users, etc). This is "total engaged users" not "engagement".