Having considered the direction of light, next let us focus on the light source.
The source of light illuminating our subject can be either a point of light or a diffuse curtain of light. The most common source of light that is a point, is the sun. (The sun isn’t a point, its actually rather large but it’s so far away that for our purposes it appears to be and acts like a point source.) Sunlight on a clear day creates a hard separation between areas illuminated by the source and areas that are not directly illuminated, i.e. shadows. Such light is often referred to as hard or harsh lighting.
(Canon 5DMII, EF24-105 @ 105mm, 1/320s, f18, ISO 400)
The other option is a diffuse light source which softens the light transitions and creates a very evenly lit subject with minimal or no shadows. A perfect example of a diffuse light source is a cloudy sky. As you might suspect, this type of light is referred to soft light.
(LG G6, 1/30s, f1.8, ISO 200)
Of course there is a whole range of light sources in between these two extremes that can provide a wide variety of light-to-dark transition abruptnesses. As the photographer it’s up to you to decide what light source best illuminates your subject and conveys the feelings you have about it.