The terms short and long confused me for years until I realised it was actually quite simple:
SHORT = something you sold to open a position, can be puts, call or stock
LONG = something you bought to open a position, can be puts, call or stock
Not to be confused with selling a LONG position you already hold or buying back a SHORT position you previously sold
When selling short the terminology is Sell To Open (STO), then Buy To Close (BTC), the converse being Buy To Open (BTO) and Sell to Close (STO)
And just to tweak
@BornToFly's comment above, when establishing a short position - which is what we mostly talk about here: "Selling TSLA Options" - you're ultimately betting the the stock moves favourably for you, which often can just mean it doesn't move at all. Options are a function of both strike price and time, you sell a call or a put for the future, if the share price were to not move at all, regardless of what you sold, you would make a profit from it whether it's in the money or not, because the time-value (also know as extrinsic and Theta) will have diminished just leaving the intrinsic value, which is the actual $$$ between the SP and the strike at expiry
So you're not necessarily looking for an option to expire out-of-the-money (OTM), just for the price not to move too much against you
This is why selling options tends to win 85% of the time - you don't actually need to be correct in your prediction/guess, just mostly right
But this isn't to say it's a free-lunch either, many of us have had trades go against us, very fast and lost hundreds of thousands of $$$, even $millions literally overnight
Trading options is incredibly risky, even when you play it safe and if you're new to it you should take extreme care, preferably do some paper trading for a while, although that doesn't evoke the same emotional response as having real skin in the game, but keep your trades very small and don't think if you get a few weeks where you win some money that you're a genius, you're not, you will get bitten in the ass at some point, and it will hurt
Really, take care and ignore what most of us do here, it's too risky for the vast majority of folks
