Sort of a baseline definition:
http://www.hazegray.org/faq/smn2.htm#B8
The problem is that the definitions are rather arbitrary, especially regarding full load displacement (and hence deadweight of a military ship).
"Standard Displacement" is about the only officially declared standard.
Edit: Just played with the dimensions and deadweight of the Trimaran LCS-2 a bit. My above estimate of 1000-1200 tons looks like it might work, if we're considering a design with an emphasis on cargo. Likely a bit more though. LCS-2 is at least twice as big as this Austal design would be, and has 608 tons deadweight, for a supposed full load of 2784 tons.