Direct sunlight would be having the sun able to shire directly on a plant for at least part of a day. Inside a house, this could happen in a sunny window, under a skylight, or in a greenhouse/solarium.
Indirect sun is when the plant would get light without the sun shining directly on a plant. Outside, it may be in the shade of taller plants all day, and inside, it might be a plant that's sitting on a table beside, but not in front of a window. It could also apply to a plant in front of a window, but with sheer curtains to filter the light.
As far as a plant getting direct sunlight inside a room on an overcast day, no. Whether it would on a sunny day would depend on where it was located with respect to windows and the angle of the sun.