At Wikipedia, “terrorist” is on their list of Words to avoid.

Extremism and terrorism are pejorative terms. They are words with intrinsically negative connotations that are generally applied to one’s enemies and opponents, or to those with whom one disagrees and whose opinions and actions one would prefer to ignore. Use of the terms “extremist”, “terrorist” and “freedom fighter” implies a moral judgment; and if one party can successfully attach the label to a group, then it has indirectly persuaded others to adopt its moral viewpoint.

In line with the Wikipedia Neutral Point of View policy, the words “Extremist”, “Terrorist” and “Freedom fighter” should be avoided unless there is a verifiable citation indicating who is calling a person or group by one of those names in the standard Wikipedia format of “X says Y”. In an article the words should be avoided in the unqualified “narrative voice” of the article.