In the credit world, piggybacking is when you allow someone with poor or average credit be listed as an authorize user on your credit card account in order to help them improve their credit. If you have a high credit score, you can list them as an authorize user, so that every time you make on time payments, it looks good on their credit report too.
There’s no need to worry about them abusing the credit card because they don’t get a card. This is just to solely help them improve their credit score. Some people make a business out of this. They get people with good credit an connect them to someone with poor credit. The person with good credit collects a fee for doing it and the person with poor credit gets an improved credit score.