Left: schematic of how energetic partons split or fragment into lower-energy prongs or branches of partons down to a scale in which hadrons emerge. An algorithm can be run over final-state hadrons to cluster them into jets. An inverse declustering algorithm can be used to recursively explore the jet substructure. Right: schematic showing that different jet axes (solid arrows) can be selected from a jet to construct the $\DeltaR$ observable. The Standard axis (represented by a black arrow) is constrained by all the jet constituents (represented by dashed arrows). The SD axis (represented by a dark blue arrow) is determined by the particles left in the jet after grooming (blue and dark red arrows). Finally, the WTA axis (represented by a pink arrow) tends to be aligned with the most energetic constituent.