Thin lines on a surface, like on a rock or in a muscle.
The word striae is usually used in science or medicine.
Examples:
The striae on the rock show how old it is.
The striae in the muscle help it move.
The striae on the tree bark are very thin.
The striae on the wall look like lines drawn by a giant!
The striae on the moon are from when it was made.
The striae on the leaf are very pretty.