A payment stream is when you don’t pay for something in one payment but rather pay in smaller amounts continuously.
You usually have a payment stream when you continuously use a product or service. You can pay for only what you use in real-time.
An example would be just paying for the energy of your house as you use it. This will allow you to have more cash as you only need to pay for what you use that day.
Think about streaming a movie on Netflix, you don’t need to download the whole movie at the beginning but you download little pieces of what you need right now which is called streaming.
Payment streams are not possible with traditional banks or fiat currency(dollars, euros etc) as the mathematical complications are too complex. You need to use a digital currency(cryptocurrency).