Majority
The query returns data that has been acknowledged by a majority of the replica set members. The documents returned are durable, even in the event of failure.
To fulfill this read concern, the replica set member returns data from its in-memory view of the data at the majority-commit point. As such, this read concern is comparable in performance as the others, but may return older data.
In a multi-document transaction, this read concern only provides guarantees if the commits in the transaction use the write concern "majority".