SE is an acronym for Serrated Edge or Spyder Edge. Spyderco's two-step serration pattern of one large and two small serrations. This pattern increases the cutting edge by 24%. Spyderco is using a pattern of 1 large and two smaller serrations. The sole exception is the C27 Jess Horn.
Some interesting information about serrations may be found in this thread on Spyderco forums.