Part of speech: Noun

Definition: one who favors restricting the functions and powers of a political organization or the achievement of a set of goals to a minimum.

Source: http://www.merriam-webster.com/dictionary/minimalist

Meaning: I read this word too while reading the article “Texting Shorthand Annoys Purists and May Have Lasting Impact”. In the sentence  Quick, inventive and utilitarian, it is a minimalist form of the language that some call irrelevant and many schoolteachers say is an insult to the English language. 

It means that some people think that using of text messaging language should be restricted or if used it should be used at a minimum.