First of all, it's 'know how', not 'know know'. You're embarrassing yourself.
And second of all; Sourced lighting, in miniature painting, is the technique of adding the illusion of a part of the miniature being a source of light. In the case of Arthas and WarCraft Undead, this would be applicable to the Runes on Frostmourne and Arthas' eyes, as well as the eyes of the skeletons, as they are shown to emit a strong icy-blue glow.
You can see the effect at work in
this still from the WOTLK intro cinematic. Arthas' eyes glow blue, and it is reflected on the trim of his helmet, as it would in real life. And
here you can see it in action on a professionally painted miniature.
What you are talking about in your utter ignorance is simple highlighting, the process of adding depth to a paint job by applying highlights and shades to otherwise flat surfaces. On this statue, you can best see it at work in the miserably painted cloak, done by drybrushing. Poorly, one might add.
Here you can see just how poor the paint job is best. He's fucking crosseyed. Not only is the signature glow effect missing, you can clearly see the different highlights. No blending applied. Second, the gold is poorly applied, there's a clear black line of seperation between the gold of the trim and the armour, with parts of the trim outright missing the gold.
This is an outright shitty paint job. It might be sufficient for whatever standard is applicable for these trash-tier quality collectibles, but that doesn't change the fact that this is a shitty paint job.