When looking through a list of prospects who opened an email, i can see under Status that some are marked as Open or Active while most are blank. What determines the status of each prospect? I've Attached a screenshot for reference
The Status field is a standard field in your instance, and it's provided so you can help keep track of where leads are in their lifecycle. Most likely you have some campaigns set up that change the field based on certain triggers, and the best way to see why a lead was marked a certain way is to look through their activity history.
Take a lead that's marked as active, open their activity log, and then open the search function in your browser (usually Ctrl+F). Then you can search for Active, or Status, and find the activity that actually changed the status. From there, you'll see in the right hand column what campaign or action initiated that change.