SSE stands for Streaming SIMD Extension, which allows, as the name suggest, processing of multiple data with a single instruction, which is best seen in the following example code:

lea   esi, [fnum1]
movq  xmm0, [esi]    ; Load fnum1 and fnum2 into xmm0 register
add   esi, 8
movq  xmm1, [esi]    ; Load fnum3 and fnum4 into xmm1 register
addps xmm0, xmm1     ; Add two floats in xmm1 to another two floats in xmm0
                     ; xmm0 will then contain:
                     ; 0.0  0.0  1.663  12.44

fnum1  dd 0.12
fnum2  dd 1.24
fnum3  dd 12.32
fnum4  dd 0.423