Lambda diagram

Lambda diagrams are a compact graphical visualization of lambda calculus with pretty much no room for interpretation.
Lambda diagrams are presented by John Tromp on his homepage here: https://tromp.github.io/cl/diagrams.html

To discern them from an extension onto the idea: annotated lambda diagrams (ALDs) as presented here on this wiki,
They basic normal lambda diagrams could also be called unannotated or "plain lambda diagrams" (PLDs)