What is the difference between marquetry and inlay?

Marquetry is decorative in its application where thin pieces of material (e.g. wood veneer, abalone shell, resins) are fixed into a shallow shape-matched recess in a workpiece, then the surface is smoothed. Wood inlay methods use thicker material and can add structural strength while still being decorative.
 
For example, our Butterfly Inlay Repair System uses inlay material that is nearly ¼” thick.  When applied over a wood crack it creates a strong “bridge” that securely holds the facing wood pieces in place.