I think I can understand this after using it.
for example, if my phone is Android, click on Mini Program, and after running, directly use the home button to return to the desktop. When you check the recent tasks, you will find that Mini Program stays in the background like an independent App. If you switch back to Mini Program (with recent tasks), it is like switching it from the background task to the foreground task. This is a hot start. On the other hand, if Mini Program is directly terminated in the recent task, or if this Mini Program stays backstage and does not move until Wechat clears it out, then opening this Mini Program will need to be reloaded, this is the cold start.