example: years ago when our house burned down, a friend of a neighbor gave us a sympathy card with $100 inside. We didn't even know this lady. When we thanked her, she just said to "pay it forward". Not long afterwards, a friend had a house fire so we gave them a card with $100 in it, asking only that they "pay it forward". During reconstruction of their house, they'd moved to a duplex, and the lady in the other side of the duplex sustained major water damage and loss from a burst pipe on her side of the structure. Soooo my friend gave her a card with $100 in it.......
That is Pay It Forward.