Theta gang just means someone who sells options and expects that option to expire worthless, thereby profiting from the slow decay of option value due to theta. It's a legitimate strategy in the options world for professionals, not just for WSB autists. Here's a random example of a finance professional running this strategy successfully in his personal account: https://earlyretirementnow.com/2019/03/27/passive-income-thr...
Disclaimer: I don't know this person, nor do I recommend copying his strategy if you don't know the options greeks; actually the amount of money you would need to execute his strategy would probably make most options beginner uncomfortable anyways.
>I use some leverage to overcome the lower premium revenue.
he uses the premium from the OTM short puts to borrow?
For example, if you want to sell an SPX put at $3000 strike, then the notional value of that trade is $300k. He doesn't have $300k in the account for that one trade though. If you want a leverage factor of 2x, then for $300k in the account you'd trade two such options, each having a margin equity of $150k. Since you're trading two options, the profit and loss are both enlarged by 2x. The worst case scenario is that if SPX drops by 50% and he doesn't take any action before that, he'd have no money left.
The author mentioned that he uses a leverage of 2x to 3x. That means you need $100k to $150k in the account to trade a single contract. Hardly for beginners.
Some people sell these contracts on the probability that they will expire worthless and they keep all the money that someone else paid for them.