Radicals, Islamists, and Terrorists?

Not necessarily. Most terrorists might be 'radical' or Islamist but the vast majority of 'radicals' and Islamists are not terrorists.

Islamists apply a certain interpretation of the Islamic sources to political realities.

Radicals might be defined as those whose views are not mainstream and conventional. It is a loose term and therefore can be misleading.

'Terrorism' and 'terrorist' are terms that are very contentious, and frequently used in ways that are politically or ideologically loaded. Over 100 definitions of the term exist. It most commonly indicates a person or a group that is not a nation-state, espouses the use of violence to achieve its aims, and targets non-combatants or civilians. The designation 'terrorist' therefore should be used on the basis of actual criminal behaviour and beliefs concerning the legitimacy of violence in different contexts.

Those who might accurately be described as 'terrorist' usually do hold political views that are 'extreme' or 'radical'. At the same time, those who hold beliefs or engage in practices that are considered 'radical' or Islamist might not endorse the use of violence. For example, the British branch of Hizb ut-Tahrir has stated that it does not support the use of violence to achieve its aims in support of a Caliphate.

Religious traits should be distinguished from these political traits. Although these political stances are inextricable from their religious justifications and form a single holistic world view, you can distinguish the religious interpretations from an espousal of terrorist violence. People who hold a strongly literalist interpretation of the Qur'an and Sunnah and reject perceived Western lifestyles, might be completely uninterested in politics and strongly opposed to the use of violence.