While reading about max flow from cp algorithm I saw this in the explanation and I really couldn't understand this :(

Here is the image I am attaching

The red line actually shows the reverse direction .

The question is how can we have a flow in reverse direction ? Here is the link to the tutorial

Lets say you have an edge from A to B of capacity 10.

Now you sent a flow of let's say 6 from A to B. So now after this flow, you have the capacity to send an additional flow of 4 from A to B but at the same time you can also take back the flow of 6 which you already sent, which in other words mean that now you can also send a flow of 6 from B to A.

Hope it clears your doubt!

Well I got it . Actually I was thinking about it like you have a valve on the other side that stops flow from B to A . Thanks :)