In this transition one shot replaces another by traveling from one side of the frame to another or with a special shape.
If the transition is to use a shape then this is chosen with theoption.
You can install new wipe files from Download New Wipes on the .
There appears to be a defect with the download new wipe files - it does not download them to where they are needed. They should go here ~/.local/share/kdenlive/lumas/HD/
but appear to go here ~/.local/share/kdenlive/lumas/
To fix manually create a HD folder and move the .pgm files there
This clip has some examples of the different wipes Kdenlive is capable of.
See also Composite Transition