Humanism is a perspective on the world that the events one experiences and observes are not attributable to the will of one or more Supreme Beings or other invisible beings, but are fully comprehensible by humans through science and other intellectual endeavors. A Supreme Being is neither necessary nor sufficient to understand the world; the intellectual efforts of humans, collectively, are necessary and sufficient.
Humanitarianism is a synonym for charity but the “ism” suffix signifies a more institutional, or at least long- standing, perspective or approach, whereas “charity” can simply refer to one-off acts as well as a broader attitude. Humanitarianism also tends to refer to a secular attitude more often than charity which is used in a religious context as well as a secular one.