I've come across the abbreviation SE several times recently. I know it has to do with the pose of the robot, and the degrees of freedom. Most recently I found it on page 8 of this paper:
D. Kragic and H. I. Christensen, “Survey on visual servoing for manipulation,” Royal Institute of Technology (KTH), Stockholm, Sweden, Tech. Rep. ISRN KTH/NA/P-02/01-SE, CVAP259, 2002.