We indicate that a participant has 'abandoned' a survey if they never reach the final page (which will either be the Thank You page or the URL that you've set).
We still include the results of any completed tasks even when the participant is marked as abandoned. We've done this because there are various reasons why participants don't complete the surveys, and this can be unintentional (like the browser session expiring). And since each task is an individual exercise, the tasks participants have already completed might be of value to you.
If you would prefer to not have these results, you can delete them from the Participants tab on the Results page.