* Hardness: Scratch-ability. If it wears or rubs against another material, does it wear out or does the other thing wear out? Chalk is one of the softest materials, diamond is one of the hardest.
* Toughness: How quickly it can absorb a lot of energy. Example: you hit it with a hammer: Not tough, it shatters (diamond). Very tough, the hammer goes 'clunk' (magnesium steel). Toughness is also called Impact Strength. Dropping your laptop is also an example of material toughness at work. (Protip: do not attempt)
* Young's Modulus: Stiffness. Very low modulus means the material is flexible and can stretch (weak plastic). Very high modulus means the material is stiff and does not bend at all (tungsten carbide). Something that is very stiff but not strong is "brittle".
* Strength: There are several varieties of strength but they refer to how much force can be applied THROUGH the material. The way to measure this is force per area. The area used is the cross section of the thinnest part of where the force will be pushing or pulling through the thing you're examining. Force per area is pressure, so strength is measured in Pounds per Square Inch (PSI), Kilopounds per Square Inch (KSI) and MegaPascals (MPa).
* Yield Strength: how much force does it take for the material to begin to bend or stretch *permanently*. (As far as most designs go, most kinds of things "are broken" if they reach the Yield point. A bent screw isn't shattered, but it can't do its job properly any more.) If you press on a paperclip, the maximum amount of push you can apply BEFORE it actually begins to change shape is its Yield Strength.
* Ultimate Strength: how much force does it take for the material to break into pieces. (Some materials, like rubber, don't have a yield strength. They just flex and flex and flex and suddenly fail.) Bending a ruler until it snaps is an example of ultimate strength for that ruler.
* Yield Limit: how much force does it take for the material to bend or stretch, AND still be able to return to its original shape. (Example: squishing a plastic cup in your hand, but not to the point where it snaps the rim.)
Different directions of forces have different names, and have different strength measurements associated with them.
* Tensile - pulling. How much force does it take to pull a thing until it bends or breaks.
* Compression - pushing or squishing. How much force does it take to squash a thing.
* Bending - self explanatory.
* Buckling - bending caused by compression of thinner parts.
* Shear - cutting action, or being pulled and pushed at the same time near the same place in opposite directions
It gets more complicated (i.e. worse) the deeper you go. I haven't even mentioned *plasticity* or *stress*, and forces can be far more complicated than just the five I mentioned.