Cock stands - not only in porn - for "cock".
Actually "Cock" translates primarily as "cock". In the porn industry or at the Dirty Talk, however, the term stands for "Tail". Many gays also use this expression to refer to themselves at the Cyber Sex flirting or each other around Cock- or Dickpics to ask.
Why many people infer "cock" from "tail" can only be guessed at. What is certain is that "Cock"has been used for so long that almost no one asks why the same term is used here. Perhaps because roosters often proudly display the feathers on their tails? Perhaps because Cock simply horny sounds? After all, this is a slightly vulgar language that often gives the impression of being dirty or forbidden.
By the way, this term is also widespread when browsing personals and chats. Many gays are looking here directly for a ONS with a "Big Cock" or send the pictures of their Cock to their chat partners. Many even use their Cock as a profile picture - a decision that does not go down well with all chat partners and all chat operators without exception.
Sending these pictures offers the advantage that everyone knows exactly what they are getting into during sex. But: of course, size is not the only decisive factor when it comes to getting a passionate One Night Stand. Rather, the "perfect" from other details, such as the correct scope and shape.
Here, as so often, everyone has their own preferences.