Having much distance from one terminating point on an object or an area to another terminating point (usually applies to horizontal dimensions; see Usage Notes below).

“It's a long way from the Earth to the Moon.”

Having great duration.

“The pyramids of Egypt have been around for a long time.”

Seemingly lasting a lot of time, because it is boring or tedious or tiring.

Over a great distance in space.

“He threw the ball long.”

For a particular duration.

“How long is it until the next bus arrives?”

For a long duration.

“Paris has long been considered one of the most cultured cities in the world.”