When becoming a Reseller you have the option to pick a bundle of 3 or 30 apps. The 3 app bundle includes 6 seats while the 30 app bundle has an unlimited amount of seats.
If you've chosen the 3 app bundle you'll be able to have 3 published apps at the same time. The amount of apps you can still publish before reaching this 3 app limit is referred to as "Apps left in bundle".
However, you might want to remove one of those apps from your bundle and replace it with another app. You can use your remaining seats to disable your published app(s). Each action you perform will use up one of your seats. The "Seats left in bundle" shows you how many actions you can perform. The "Apps left in bundle" shows the amount of apps you can still publish at that time.
The seats are reset each year.
When you've purchased a 3-app Reseller bundle, also known as a small bundle, you start off with 6 available seats, and 3 available apps in your bundle.
When you publish 3 apps, your seat count will drop to 3, and your available app count will drop to 0.
When you decide it's time to deactivate 1 of your published apps, you can use a seat to perform this action. Your app count will then be changed to 1 again, allowing you to publish a new app.