The BoxedIce guys are continuing their series on Monitoring MongoDB, this time explaining parts of the
db.serverStatus(): connections, index counters, background flushing (nb this is the part where MongoDB can lose your data), and opcounters.
db.serverStatus() is similar in a way to MySQL
SHOW VARIABLES LIKE 'Inno%' and
SHOW ENGINE [INNODB] STATUS.
These aside, I assume this whole series is just a preamble for their upcoming MongoDB monitoring service.
Original title and link: MongoDB db.serverStatus() Explained: MongoDB Monitoring (NoSQL databases © myNoSQL)