Repair and deduct is when you tell your landlord that something needs to be fixed in your home, like a leaky faucet or a broken light, and they don't fix it. So instead of waiting for them to fix it, you hire someone to fix it yourself and then you take the cost of the repair out of your rent.
It's like when you have a toy that's broken and you tell your mom or dad that it needs to be fixed but they don't fix it right away. So instead of waiting, you fix it yourself with some tape or glue and then you subtract the cost of the tape or glue from your allowance.
But remember, you shouldn't just go and hire someone to fix things without talking to your landlord first. You have to give them a chance to fix it themselves before you can do it yourself and take the cost out of your rent.