They can appear in certain video games and similar games where players can make a purchase to receive further items to assist them in playing the game. A loot box is also referred to as an in-game purchase and is entirely optional. A player will pay a set amount to obtain a loot box, which will have a series of virtual items inside. This is then 'delivered' to them within the game.
What will you find in a loot box?
It depends on the game you are playing. Sometimes, you might get bonus items that can be used to help you make successful moves to complete levels. Other times, a loot box might contain clothing and other items you can use to personalize your character (avatar) if one is included in the game. If the game involves combat scenarios, your loot box might contain weapons for your character to use.
Some games will have boxes you can buy, while others include locked loot boxes that are found as you play the game. In this case, you might collect the boxes and then choose to purchase keys to unlock them if you wish. While some games permit players to buy look boxes with real cash, others offer them in exchange for coins earned within the game. As such, the latter does not require a real payment to be made.