Oh boy, we had a very long topic on this one. Its a ship prefix like U.S.S. or H.M.S., but as to what it actually stands for we don't know (nor could the community agree on what sounded best).

Edit: Found the old topic. My bet is on Trader Defense Navy, but you can see the others there as well, in addition to a Dev refusing to tell us the secret.

Here's a recent topic too

It's been speculated on before, but there's no real confirmation.

The most commonly suggested one is "Trader Defense Network"

I think it stands for Trader Defense Navy.

Not again!

Well yes, it just that this issue has been beaten

like this

There's a point when you get mildly annoyed at the whole thing.

sorry

However the 'S' at the end of both of those stands for "Ship".