What is the term used to describe the percentage of users that don't continue in a flow?
For example, if only 50% of users go from the login screen to the profile screen, what do you call that?
It depends on the context, but these are often used interchangeably.
A few options are:
More on the distinctions (from a web analytics standpoint) on:
There are definitely a lot of terms for it and it really depends on the context.
In many cases you have a new user funnel. There may be a certain step that you may consider that user an customers, player (if a game), etc. That would be the conversion rate.
If you don't have a flow and you have users coming to the page and leaving immediately, that would often be referred to as the bounce rate.
If you have a custom flow as you are describing. This is often called the drop-off rate.
In some flows, especially if dealing with subscriptions (mobile / social apps included) this would be considered as the churn rate as users leave and never come back / remove the app.