A stria is a thin line, especially one of many that are parallel or close together.
The word stria is often used in science and medicine to talk about lines or marks on things.
Examples:
The rock has many colorful strias.
The stria on the leaf is very thin.
I see a stria on the glass.
The strias on the zebra are black and white.
The stria on the butterfly's wing is very beautiful.
The strias on the water are moving fast.