Clich here for images of plain cis & trans resveratrol. (Those piceids have a 6 carbon sugar added to cis & trans resveratrol.)
That trans is used in the same sense as trans fatty acids, aka trans fats. It refers to how parts of a molecule with a carbon to carbon double bond, the two in the middle with a double line. Cis means those modified benzene rings are on the same side of that middle carbon double bond. Trans means those modified benzene rings are on opposite sides of that middle carbon double bond.
Plain benzene, C6H6, is often shown as a hexagon with a circle inside of it. A carbon is at each vertex of the hexagon, and hydrogen is assumed.
That's your organic chemistry lesson for the day. You're welcome. I linked the images of cis & trans resveratrol because it's an oversize one.