A violent Vulcan fringe faction of the twenty-third century that regarded humans and the Federation as a contaminating influence and used bombings and assassination to pursue what it called pure logic.
The logic extremists are a small Vulcan movement who believe that contact with humans and other emotional species is corrupting their world, and who are prepared to kill for that belief.
Star Trek: Discovery shows that they bombed the Vulcan Learning Center when Michael Burnham was a child because a human was being educated there. In the episode Lethe a member named V'Latak makes a suicide attack on Sarek's ship as the ambassador travels to secret talks with Klingon houses, leaving him critically injured.
The second season reveals that the faction's sympathisers reached high places: the Section 31 admiral Patar is described as a logic extremist in Project Daedalus.