P&L (profit and loss)
P&L, also written PnL, is the profit or loss of a position, in money. For a long it is (exit price minus entry price) times quantity; for a short, (entry price minus exit price) times quantity.
While a position is open, its P&L moves with every tick and is called unrealised: it is only on paper. When you close the position, it becomes realised and lands in your balance, minus fees. A long of 10 shares bought at 350 and sold at 360 has a P&L of (360 minus 350) times 10 = +100.
Learn more: long and short positions.