Twists are two strands wound together, with extension added at the root. Senegalese are twisted tight and rope like, marley are matte and textured, passion are wavy and soft.
They install faster than braids and come down faster too, which is why they are often the first protective style someone tries. The shorter versions are also the cheapest thing on most menus.
They are also the loosest. A twist unwinds where a braid holds, so the ends matter and so does the sealing.
Less time in the chair, less time on the takedown.