"Lightweighting" is what Autodesk, the supplier of the world's leading computer aided design (CAD) software, labels a design strategy for making products with less material.  Here's how they describe it:  

Lightweighting means optimizing your design’s geometry and structure so that it uses less material. Products made with less material have less negative environmental impact, from production to disposal. For every pound of material you save, you eliminate much more material waste upstream – and light weight products and vehicles use less energy to move. Learn engineering best-practices for reducing material use while maintaining the structural integrity and manufacturability of your designs. Some strategies include hollowing parts and decreasing wall thickness, using reinforcements like ribs and posts, using trusses, avoiding stress concentrations, following lines of force, and using tensegrity.

Autodesk produces and shares engaging videos explaining lightweighting.  As a CAD software company, it makes sense for them to educate designers who might then use their software to lightweight a material or a design.  (See below for a sample video and links to others.)

We're likely to see more dMASS strategies like lightweighting in the future as it becomes more apparent that a sustainable future requires delivering much more function with much less mass.  Though it's not yet happening on a wide enough scale, the idea has been active in design for some time.  Consider the history of the aluminum can as an example.

About 50 years ago, beverage cans were made from tin-plated steel and they had seams.  The aluminum industry developed a new method for making seamless cans, but aluminum is much more expensive than steel or tin.  Every gram of mass built into the can meant more cost.  The Aluminum Company of America (ALCOA) answer was lightweighting:  designing a can to use the thinnest aluminum possible while still delivering the requirements for strength and appearance.  ALCOA's materials researchers invested considerable trial and error in trying to thin down the sheet.  It was art more than science.  They were able to reduce the thickness of cans further with the advent of computer modeling.  ALCOA continues today to apply lightweighting research and design strategies in the automotive industry

You can view the Autodesk lightweighting videos here.  Here's one to get you started: