A promo code is short for promotional code. It is usually for a discount towards a special that a business is having. It is basically a type of coupon that merchants offer. They can be used for different services or items that companies provide. Sometimes, there are discounts available on-line (internet) that aren't available in stores. Promo codes are entered during checkout whether online or in person. Some can be printed out and used in person, some can be sent to your phone, but the majority of them are strictly for on-line shopping. Promo codes can offer you a percentage off (i.e. 20% off) of an item or service, a dollar amount off (i.e. $10 off), and even free shipping. I've even seen promo codes to by an item, get an item free or buy one, get one half off. There are so many out there.
They are also referred to as: