A description of how much the cushions in plates respond to changes in force applied.  High action would describe a plate-cushion configuration that moves easily while low action would describe a less mobile plate-cushion configuration.  Action can be adjusted by loosening/tightening the nut along the kingpin that compresses the cushions.

In shoe-making a counter is the little heel cup

Counters are physical additions to a skate boot that adds rigidity.  They are a complex of material stiffeners, cement, fiberglass & epoxies, and/or carbon fiber.  You can usually feel what materials may make up a proper counter in the heel cup of a skate made by a reputable manufacturer.  Counters can be made more or less stiff by varying the kinds and quantity of stiffeners.  Counters exist to counter skaters' entire bodyweight agianst bending/warping boots structures from high torque/force movements like jumps, spins, and slides.

Newer skaters say a what they perceive as a stiff boot provides them ankle support, this is not accurate.  More often than not, they are not willing to push against them since they will hurt. That fear of pain changes their behavior infinitely more than the boot provides support.  Now you know better.

A measure/scale which quantifies the hardness of a material, typically of polymers, elastomers, and rubbers.  Measures range from 0 to 100.  In skating, the Shore A and Shore D scales are commonly used.

• diagram of the indenters

• Shore OO, A, and D scales

A synthetic clay material used to create hard roller skate wheels.  Clay is mixed with polymers to improve elasticity ultimately improve durability.  Modern FM wheels are slightly less hydrophilic compared with Vintage FM wheels but it is recommended to not have them stand in water for an extended period of time.

In a nutshell, using boots that are outside of your weight-class (in skill and in weight).  

The hole where the pivot pin or "nose" rests. 

* note: non-precision pivot pins are also known to have a pivot pin bushing, since they are made of rubber

Measured in percent (%), the slip-grip ratio gives general probabilities of a stride to have traction verses no traction (slip).  Wheels may have high traction (grip) or low traction (slip) in particular environmental conditions.  A particular class of wheels are grouped together—e.g., Fo-Mac Slicks, Fo-Mac Minis, and Fo-Mac Harmonys are classed under Fo-Mac—when describing slip:grip.  

I.e., Fo-Mac wheels have a 40:60 slip-grip ratio on well-coated maple floors.

Speed rings are small washers, that match the size of the inner part of the bearing. They increase the space between the bearing & wheel, preventing contact friction, ultimately allowing the bearing to do its job and spin more freely.