Cold calling is when someone you don't know calls you on the telephone to sell you something, without you asking them to call you. It's called "cold" because the person calling doesn't know you and you don't know them, like when you see someone you don't know at the park.
Sometimes people use cold calling to try and sell things like vacations, insurance, or credit cards.
Not everyone likes getting cold calls, because they can interrupt what you're doing and you might feel pressured to buy something you don't really need. But sometimes, cold calls can be helpful if you're looking for something specific or want to learn about a new product.
So, the next time the phone rings and you don't recognize the number, it might be a cold call!