Could anyone tell me about masking and unmasking in ACL?

[Nithya Devi]

Could anyone tell me about masking and unmasking in ACL?

[abbasshaik4]

Hello @Nithya Devi,

Masking: An Access Control that was effective until you made a change. 
Unmasking:  An Access Control that was made effective when you made a change.

Please refer to the below link:
https://docs.servicenow.com/bundle/washingtondc-platform-administration/page/administer/general/conc...

Mark my correct and helpful, if it is helpful and please hit the thumbs-up button to mark it as the correct solution.
Thanks & Regards,
Abbas Shaik