"An item of value, money, or documents deposited with a third party to be delivered upon the fulfillment of a condition. "
For example: The buyer would give the money to the Escrow Service for the goods and the Escrow service gives the money to the seller once the goods are delivered.
The third party helps to ensure that both of the interested parties receive the product/service/payment involved in the transaction. This helps to prevent a situation where the buyer sends the money and then the seller takes off with the cash and never delivers the goods....
Escrow services are most commonly used for larger amounts but even a pseudo escrow services, that is trusted by both parties, can be used for the smaller ones.
My kids, for example, use Escrow all of the time lol. I have three kids... when one is trading a candy bar for a glass of chocolate milk (thanks to a mistake made by youngest long ago which involved something like quickly guzzling the milk and then not giving up the candy bar), they now give the milk and the candy bar to the third uninvolved child who then delivers the goods to the receiving party. One child does not receive the candy bar until the other child has given up the milk and neither can cheat the other since the third child is on the receiving end until both items are received..the third child then can deliver.
Lucky for them, the third child is honest...otherwise they'd both be out of luck with the candy and milk