Political correctness (or PC for short) means using words that will not offend any group of people.    Some offensive words have been used for a long time.  Some of these words have now been replaced by other words that are not offensive.  These new words are described as politically correct.

The term is often used in a mocking sense when attempts at avoiding offense are seen to go too far.

History 
This term has been used since the early 1970s. It started being used in the modern negative sense in the late 80s in America.

Examples 
Politically correct words or terms are used to show differences between people or groups in a non-offensive way. This difference may be because of race, gender, beliefs, religion, sexual orientation, or because they have a mental or physical disability, or any difference from what most people believe is normal.

Political correctness with gender 
Throughout the 20th century Feminists fought for women to have the same rights as men.  In PC language this is seen in changes to job titles such as "policeman", "postman", and "chairman" which now commonly go by the gender-neutral titles "police officer", "letter carrier" and "chairperson" or "chair" as well as with terms having broader application, such as "humankind" replacing "mankind".

Political correctness in sexual attraction 
People who are attracted to the same gender are usually referred to as 'homosexual'. Likewise, people who are attracted to people of both genders are usually referred to as "bisexual". However, both of these terms are seen as being perfectly fine by the more politically liberal oriented people.

Political correctness in medicine 
People who are mentally disabled are now rarely described as "mentally retarded" (sometimes called "M.R.") but may be said to have "special needs". M.R. has been changed to I.D.; Intellectual Disabilities.

People with significant vision loss are called low vision or blind. 
People with significant hearing loss are called deaf and/or hard of hearing. 
People who cannot speak are no longer called "dumb", they are non vocal. Those who are vocal but cannot communicate fluently are called non verbal. 

The overall terms 'handicapped” or 'challenged' are not  considered appropriate (there is no distinction between physical or mental, acquired or inborn, because unless you’re the disabled person, it’s your choice to disclose and confirm whether this matters)   
Person first language is “ Sarah has physical disabilities”. This is part of the medical model of disability, which suggests disabled people are something to be fixed, even if there is no pathology to suggest “fixing”. 

The social model of disability encourages identity first language (Sarah is disabled) and is not just preferred by most of the disabled community but is also part of the social model of disability. The social model of disability invokes (rather than erasing as medical model does) the idea that disability isn’t just about limitations within daily life but also acknowledges that most of what creates disability are the social and infrastructural challenges faced, such as inaccessible housing, sidewalks, elevators.

Criticism 
Some of the new politically correct words are often criticized for being rather ridiculous. Some examples of these are the terms ending in challenged. For example, someone who is very short might be described as "vertically challenged".  People also say that things that are obviously bad are called by something else which hides the fact that they are bad. For example, young people who are in trouble with the law, instead of being called "juvenile delinquents" became "children at risk".  Some PC terms may be ambiguous i.e. have two possible meanings. "hearing impaired" can also refer to someone who has partial hearing (hard of hearing) and "vision impaired" can also refer to someone who has partial vision.

Related pages 
Discrimination
Identity politics

Wikiquote has quotes related to political correctness.

Linguistics  
Human issues