I'm not aware of any documentation of the individual trace events... I'd recommend reading up on some of the
design docs, e.g. on rendering if you're interested in understanding blink/rendering-related work further..
this section might be a good starting point.
Apart from that, doing a code search for the event name like you mentioned should give you some context of the work it annotates.
Depending on your use case, there's also the
devtools timeline tool, which is geared towards web developers and may present trace data in an easier-to-digest way.