What is the meaning of 'dec' in this circuit simulation file?

* .PRINTALL directive means: save all voltages and currents
.PRINTALL

* .TRACE directive define the simulation windows
.Trace AC VDB(OUT) VDB(X) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace AC VP(OUT) VP(X) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace DC V(X) V(OUT) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace DC I(R2) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace Noise DB(ONOISE) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace Tran V(IN) V(OUT) V(X) Min=-1.0000000e+00 Max=3.0000000e+00
.Trace Tran V(IN) {D = ABS(V(X) - V(OUT))} Min=-1.0000000e+00 Max=3.0000000e+00
.Trace Tran V(OUT) Min=-1.0000000e+00 Max=3.0000000e+00

* Accuracy and analysis directives:
.Eps 1m 100m 1u
.H 1fs 1fs 100ns 250m 2
*.TRAN 100N 100U 0
.Tran 100ns 100us 0s noise=yes noisestep=500ns traceBreak=yes compress=no compressCoeff=1 compressTolX=0 compressTolY=1u powerup=no timeup=0s predict=no
.AC dec 5 100 10MEG op=no
.Noise V(OUT) VIN 10 100 10MEG op=no compress=no compressCoeff=1 compressTolX=0 compressTolY=1u
.DC VIN 0 5 0.1

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