Long position
A long position is a trade that profits when price rises. You buy first and sell later, so to close a long you must sell, whatever the price has done.
Buy 10 Tesla shares at 350 and sell them at 360, and the long made 10 per share, 100 in total. The most a long can lose without leverage is what it cost, if price falls to zero. “Long” says nothing about how long you hold: a long can last ten minutes.
The opposite is a short position.
Learn more: long and short positions.