Self weight is the load on a structure imposed by its own weight. Self weight is directly influenced by the material density of the structure. By default, self weight is turned off and needs to be enabled if it is to be modelled.
The selfweight will depend on 1) the material and 2) the section of each member. It is recommended to double check the materials and sections used within your project so that the self weight of your structure is as accurate as possible.
The self weight form allows you to specify multipliers to acceleration due to gravity (g) in the X, Y, and Z axes. If switched on, the default self weight acts in the Y axis with a magnitude and sign of -1.