In civil engineering, specified loads are the best estimate of the actual loads a structure is expected to carry. These loads come in many different forms, such as people, equipment, vehicles, wind, rain, snow, earthquakes, the building materials themselves, etc. In general, these loads can be divided into two major classes: live loads (loads which are not always present in the structure) and dead loads (loads which are permanent and immovable excepting redesign or renovation).
A good example of specified loads would be the following simplified floor to ceiling sandwich load table (based on the National Building Code of Canada standards):
Floor Finish (Terrazzo) per 10 mm thickness = 0.24 kN/m^2
Reinforced Concrete per 10 mm thickness = 0.24 kN/m^2
Mechanical Services = 0.35 kN/m^2
Electrical Services = 0.10 kN/m^2
Floor Area (110 mm thickness) = 8 m^2
Total Dead Load = (0.24 + 11*0.24 + 0.35 + 0.10)*8 = 26.64 kN
In order to design to these loads, one would need to convert them to design loads by applying Load factors or, more generally, a form of safety factors to them. In the case of limit states design, the resulting factored load is then called a Design load. Note that in this case of Limit states design, we would refer to the factor as a load factor rather than a safety factor in order to try and eliminate possible confusion between Limit states design and the older Allowable stress design.