Amanda takes a stab at it, and explains it well with nice and simple charts and graphs.
Think of a flash cell as a kitchen sink. One side is called the source, regard it as the faucet. The other side is the drain, which works just like a real drain. In between the source (faucet) and drain is a gate blocking the flow of electrons (water). When the gate is closed, there is no electrons flowing (water) between the source (faucet) and drain.
Thanks to Amanda for breaking it down for us.
Note: Be sure to check out Amanda’s other site: Feeding the News Beast filled with amazing historical photos of the TV news business in the early years.