Although "cushion" as a wet shaving term has never been defined explicitly, I consider cushion to be similar to the term "lubricity" as used by engineers to measure the way a lubricant can protect parts from premature wear. Lubricity can be considered an "anti-wear" property. Some lubricants protect against wear better than others.
Similarly, I use the term "cushion" to represent the ability of a soap to protect my skin from "wear" and irritation due to the pressure of a razor blade during shaving. While the overall pressure applied by the razor to the skin is quite low, when you consider that the contact edge of the blade against the skin is less than 1 micron wide, the pressure measured in grams per square mm of contact area is rather high. An excellent lather will provide a very thin layer of lubrication between the contact edge and your skin to protect your skin cells from damage.
For those with sensitive skin, excellent "cushion" is required to protect the skin from irritation. However, I have had discussions with others who have had less sensitive skin who believe that a lather with "cushion" prevents them from getting a super close shave. I believe both viewpoints are valid.
Similarly, I use the term "cushion" to represent the ability of a soap to protect my skin from "wear" and irritation due to the pressure of a razor blade during shaving. While the overall pressure applied by the razor to the skin is quite low, when you consider that the contact edge of the blade against the skin is less than 1 micron wide, the pressure measured in grams per square mm of contact area is rather high. An excellent lather will provide a very thin layer of lubrication between the contact edge and your skin to protect your skin cells from damage.
For those with sensitive skin, excellent "cushion" is required to protect the skin from irritation. However, I have had discussions with others who have had less sensitive skin who believe that a lather with "cushion" prevents them from getting a super close shave. I believe both viewpoints are valid.