What is the largest magazine subscription?

I'm curious to know, what exactly constitutes the "largest" magazine subscription? Are we talking about the most widely circulated magazine, or perhaps the one with the highest number of individual subscribers? Additionally, is there a particular metric that the industry typically uses to measure this, or does it vary depending on the context? I'm eager to understand how one would go about determining the largest magazine subscription, and if there's any data available to support such a claim.