A Replication - Latency alarm alerts you when latency on the Distributor or Log Reader agent exceeds a threshold.
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Latency is the amount of time that elapses between a command being committed at the Publisher and the corresponding command being committed at the Subscriber. It is a key measure of the performance of your replication environment, especially when data must be available at subscribers within a certain time period to meet service level agreements.

When this alarm is current, open the Activity drilldown | Agents page to see which agent is experiencing high latency times.