In solidworks help Factor of Safety distribution is defined as:

To plot the distribution of the factor of safety.

Areas of the FOS plot with values larger than 100 are shown with the color of the 100 value. If the maximum FOS value is less than 100, then the chart is scaled from the minimum to the maximum FOS value.

I dont understand it. What do they exactly mean?

The FOS is defined as: (Allowable Value)/(Calculated Value). The allowable value is based on the failure theory (Tresca, von-Mises, Mohr, etc.) and the property value associated with the respective failure theory (maximum shear stress at yielding, yield strength, ultimate strength, etc.)

For example, if you have a part made of A-36 steel:

Several things to keep in mind: