Lifetime Hosting means that MyPhotoApp will host your active apps, even if you stop subscribing to MyPhotoApp, forever.
Active apps are apps that are in use... used at least once over a 2 year period. If an app hasn't been used in over 2 years, then it is consider abandoned and will be subject to be deleted. But as long as people are getting use out of the app, MyPhotoApp will continue to host it. Some professional features, like forms, will stop delivering when you stop subscribing.
Lifetime hosting is an option that you can purchase at time of subscription. It is only available with yearly plan subscriptions. Monthly plans do not have a lifetime hosting option.
If you should stop subscribing, the last plan you are under applies to all of your apps regardless of which license type you created them under. For example, if you currently do not have a lifetime hosting subscription and switch to a lifetime hosting subscription, all of your apps will fall under the lifetime hosting. If you are currently under a lifetime hosting plan, but switch to a license that does not have lifetime hosting, then all of your apps will no longer be hosted if you stop subscribing.
If you currently do not have a lifetime hosting subscription and you desire lifetime hosting for your apps, you can just purchase a subscription with lifetime hosting, or you can turn your plan into lifetime hosting at any time prior to your subscription expiring by just paying an upgrade charge (currently $100).
You can see what subscription you have on the license tab of the builder.