CAN against a passenger means that passenger’s ticket no longer exists. It appears when you cancel online, when a fully waitlisted e-ticket is dropped at charting, or when the railway cancels the train and refunds the booking. CAN/MOD together means the booking was modified after a partial cancellation, for example one passenger removed from a group.
A cancelled status is final for travel purposes. The refund that goes with it depends on why it was cancelled: the slab rules for a voluntary cancellation, clerkage for a waitlist drop, and a full refund when the train itself was cancelled.
Also written or searched as: cancelled ticket · CAN status · CAN/MOD