What is ment by "Transition Period"? and when this period starts and when it ends?

When reading about Power Platform requests limits such as those links:-

 

 

 

There always something called transition period so what is this period? and how i can know if our organization is in this transition period or not? i have a tenant i have been working on for 3 years and i got an email from Microsoft last week mentioning the transition period, so does this mean that a tenant which was create more than 3 years ago and which uses power apps and power automate since that time is still in this transition period??