As simple as it can be,
Threading is about workers & asynchrony is about tasks.
Real Life Restaurant Example
An analogy usually helps. You are cooking in a restaurant. An order comes in for eggs and toast.
- Synchronous: you cook the eggs, then you cook the toast.
- Asynchronous, single threaded: you start the eggs cooking and set a timer. You start the toast cooking and set a timer. While they are both cooking, you clean the kitchen. When the timers go off you take the eggs off the heat and the toast out of the toaster and serve them.
- Asynchronous, multithreaded: you hire two more cooks, one to cook eggs and one to cook toast. Now you have the problem of coordinating the cooks so that they do not conflict with each other in the kitchen when sharing resources. And you have to pay for them.