Heliotropism is a scientific term for a plant's tendency to turn toward the sun. Sunflowers are well-known for their heliotropism — they move in the sun's direction over the course of a day, tracking it across the sky.
Have you ever noticed a house plant growing in the direction of a window? This is an example of heliotropism, when certain plants (and a few other organisms, like fungi) prefer to face the sun and grow in the direction of sunlight. This works with artificial lights as well, and in that case it's known as phototropism. We can trace heliotropism back to the Greek roots helios, "sun," and tropos, "a turn or change."