Explain what is meant by the "Euphemism Treadmill"

The Euphemism Treadmill is a concept coined by Stephen Pinker in his 2003 book "The Blank State". The concept explains how words that are used to replace offensive terms over time become offensive themselves. For example, the word "retarded" was introduced as a 'kinder' alternative to the term "imbecile". However, "retard" has since become just as offensive, and has now been replaced with words such as "special needs" or "intellectually challenged".

Pinker's Euphemism Treadmill serves as a prediction of possible offensive terms in the future, perpetuating language change and serving as an example of how the sometimes considered 'restrictive' nature of Political Correctness is, in and of itself, unrestrictble, and constantly subject to change.