All the above 4 things define how data will flow between target and source objects when WPF
binding is applied.
Two way: – Data can flow from both source to target and from target to source.
One way: – Data flows only from source to target.
One way to source: – Data flows only from target to source.
One time: – Data flows only for the first time from source to target and after that no
communication happens.

one way, two way, one time and one way to source