I obtained several statistics from runs of Z3. I need to understand what these mean. I am rather rusty and non up to date for the recent developments of sat and SMT solving,
I am afraid this is an open-ended question. Z3 exposes many counters that are collected in many different ways. While many capture abstract concepts, their meanings are ultimately based on implementation behaviors of the code.
Fortunately the source code is available and provides the full context for understanding the behavior of each counter. So there is no single document that tracks the meaning of the counters, but the source code is made available to give the full context.