I am afraid there was barely anything to write about here, so again I've resorted to using a latin phrase.
Quid pro quo is associated with contract law, and is a latin phrase meaning 'this for that'. It refers to something that is given in exchange for something else. A contract is enforceable in court, and regulates literally everything in our society, from buying tickets to paying for a service (e.g. roof repairs, where you will give consideration in the form of money to someone who will provide a service to you, that being fixing your roof).
Quid pro quo is basically the same/similar to 'consideration' - one element needed when establishing whether you have an enforceable contract. This basically means that you exchange something of value (money), for something else of value (a service such as roof repairs).
So another example would be, Adam (A) goes to the shop to purchase a product, and Boots (B) sells him the product. A will provide something of value (money) for something else of value from B (the product).