To randomize is to let chance decide who or what goes where — on purpose, because a fair test needs that. In a medical trial, you do not let the doctor pick the groups; a computer or a chance method does, so one group is not quietly healthier than the other. Scientists, doctors, and people who work with numbers use the word; it feels technical, not chatty. Though actually, everyday English stretches it: people randomize a playlist or a seating list, meaning they shuffle it. That looser use is real, but the careful meaning is the test meaning: chance used as a tool, not mess for its own sake. American spelling uses -ize; British English often writes randomise. The meaning does not change.