The load moment
for a crane is a number measuring the weight of the load lifted times the distance between the mass and the centre of the crane's superstructure
. For example, a 20 ton weight lifted at 5m away from the crane (in reality, right next to it!) gives us a load moment of 100 ton*m, the same as a 10 ton weight lifted 10m from the crane. Cranes can handle higher load moments closer to the crane, so really heavy lifts are always done from very close to the load.
Similar to the load moment is the "overturning moment", which measures how much weight at a given distance (from the nearest part of the crane, not the center) results in the crane tipping over! Due to the weight of the boom etc., this usually means the load that can be lifted is less than the rated load moment would suggest. Outriggers (the legs which extend out from the sides of a crane truck) decrease the effective distance from the crane to the load, and thus reduce the overturning moment for a given weight.