Some explanation needed for some metrics exported to Prometheus

Been recently checking some Prometheus metrics exported by Percona and need to explanation regarding what means what and from where does it come (if possible).

mongodb_mongod_op_latencies_ops_total and mongodb_mongod_op_latencies_latency_total.

Also, apart from those two… In a WiredTiger cluster when executing db.serverStatus(), within wiredTiger, perf. Checking the “file system read latency histogram” keys… Does that latency mean read times elapsed until the data sector is found?

Thanks in advance!