>>4369427>>4368211I think flat means unshaped. If you use flags to shape the lighting it becomes dynamic lighting. If you do nothing to control the light hitting the subject to give it shape or texture or something to make it interesting to the viewer it is flat.
Narrative film makers normally use dynamic lighting.
People doing beauty shots or product shots use flat lighting and people doing a make up tutorial video use a ring light to make the lighting extra flat because they want you to focus on the make up on the face of the model and not on the lighting they used to illuminate the face.
If you block part of the ring so only part of the face is illuminated it becomes dynamic lighting because you focus on the lighting effects and not on an evenly lit face.
I hope my long autistic rant about lighting helped you.