Conversion marketing is when grown-ups try to convince other grown-ups to buy things. It's like when you go to the store with your mom or dad and they try to get you to pick the Cheerios instead of the Froot Loops.
But with conversion marketing, instead of Cheerios and Froot Loops, they are trying to sell things like clothes, toys, or even vacations to other grown-ups. They do this by finding people who might be interested in what they are selling and then showing them pictures or videos, or telling them how great the thing is.
Once someone is interested, the goal is to get them to actually buy the thing. This is called "converting" them from just being interested to actually buying it. Sometimes grown-ups offer special deals or discounts to try and convince people to buy.
Overall, conversion marketing is all about trying to make sure that people who might be interested in something actually end up buying it.