means A graphical or written sequence of events arranged in the order they happened, used to show how things unfold over time.

from A transparent compound of "time" and "line" — "time" from Old English tīma (a span or season), and "line" from Latin linea, "a string of flax" and so a drawn thread. The word itself is a relatively modern coinage, appearing in the late 19th or early 20th century when people grew fond of plotting history as a straight measured rule. Its social-media sense — the endless scroll of posts — is a 21st-century descendant, the same straight line now running vertically off the bottom of your screen.