Diagrams showing relationships between things (6)
I believe the answer is:
graphs
'diagrams showing relationships between things' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for graphs that I've seen before include "Drawings with quantities ploted on axes" , "Diagrams showing relationships between things" , "Charts" , "Diagrams with horizontal and vertical axes" , "Diagrams that show ratios" .)