Riley is a statistics gathering and reporting library for Java, designed to be high performance and thread-safe. It provides an API which allows applications to report events and configure how often and the format of Rileys output.
Performance measurement and monitoring is quite often an afterthought when developing an application but once deployed to production the same questions get asked time and again. Knowing exactly how fast it's taking to operate is vital to knowing where to devote time and effort into increasing throughput and scalability.
"Event" == Something that happens.
The first and most basic measure is a simple total of how many times an operation has occured since the application was started. It's important that Riley knows the lifecycle of the application.
This relates to the Totals because a common question is "How many times an has occured per hour (or minute, or day, or any time period)?". Riley knows when the application was started and it knows the current time thus is can output average number of events over these time periods.