This term refers to "Case Management/Electronic Case Filing."
This an "electronic filing" procedure that only applies to attorneys.
If you are filing for bankruptcy without an attorney (also known as filing 'pro se'), you can safely ignore all the warnings about "mandatory CM/ECF" -- you are not required to file electronically.
If you are an attorney, don't worry. This procedure is not as complicated as it sounds. In most districts, it basically means that the forms must be saved as PDF files and submitted in a specified manner.