This phrase is used to politely ask someone to speak or do something more slowly. "ゆっくり" means "slowly." It's very helpful for beginners learning Japanese when native speakers might be speaking too quickly to follow. You can add "すみません" for extra politeness.

相手にゆっくり話したり、何かをゆっくりしてほしい時に使う丁寧な表現です。「ゆっくり」は「速くない」という意味です。