MRR is Monthly Recurring Revenue. This takes into account all the ACTIVE and Non-Renewing Subscriptions.
CMRR is very similar to MRR but this also includes any pending changes that are due within this month.
Fundamental difference is that: MRR is based on as-is state vs. CMRR which is a projection based on pending changes within this month.
Example: If a customer has a scheduled cancellation at the end of current month's billing cycle, MRR will still include that customer's recurring charges in calculation, whereas CMRR will not.
Here is a blog that explains, the basics of MRR calculation.
Are Subscriptions in "Future" state and "In Trial" included in the calculation?
They are NOT included in MRR calculation.
However, if the "Future" Subscription is scheduled to become "Active" within the current billing month, then they are included in CMRR.
Similarly, if the "In Trial" subscription is scheduled to generate a recurring charge within the current billing month, then it is also included.
Note that, these subscriptions either needs to have a valid card or be marked as "offline subscription" to successfully move to "Active" state.