diff --git a/3D-printing-101.md b/3D-printing-101.md
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 # 3D printing
 
 * .f3D = Fusion360
-* .ipt = Inventor 2021 design file 
-* .STL = just 3D shape
+* .ipt = Inventor 2021 design file
+* .STP STEP (or STP) is a popular file format used to store and transfer 3D and 2D geometry models, parts, and design data.
+* .STL = 3D print print file
 * .3MF = 3D print slicer file
 * .gcode = prusa file?