Majority
Requests acknowledgment that the calculated majority of data-bearing voting members have durably written the change to their local oplog. The members then asynchronously apply changes as they read them from their local oplogs.
This value is the default for most deployments.
After a write operation has received a majority acknowledgment, clients can read the results of that write with a ReadConcern.Majority read concern.
External resources
See also
Specify this option.