The name “Slack” has always felt like a wink and a nod. The popular messaging service is designed to replace traditional office email and increase productivity, but it can also be fun to the point of distraction. Hence the irony in what Slack terms its users (“slackers”) and how it’s come to be used as a verb (I’m slacking).

But it turns out that Slack is an acronym as well. It stands for Searchable Log of All Communication and Knowledge.

Slack co-founder and CEO Steward Butterfield revealed that last night in response to an inquiry on Twitter. He included a screenshot of a chat from Nov. 14, 2012, in which he announces having come up with “a better code name” for the program.

Clearly, the codename stuck.

Butterfield’s uncommonly candid persona and Slack’s smooth interface have made the company a media darling, as well as one of Silicon Valley’s best-known “unicorns.” Slack closed its most recent round in April, bringing its funding total to $540 million and its valuation to $3.8 billion. At the time, Slack said it had 2.7 million users of which around 800,000 were using a paid version of the service—that is, a truly searchable log of all communication and knowledge.