I assume that it’s the “recent read time” stat in your user summary, but that just punts your question to another, related question.
My guess has always been that this is some count of “active” browsing time through articles and topics, or something similar. I bet @codinghorror could give us the specifics…
Not-a-mod-note that we’re wading into Q&A on Non-Moderation Matters territory…
