Okay I’m no expert or anything but it’s similar to regional accents in any language, people from different areas just use some different words, pronunciation, intonation, and grammar. However, they are considered dialects rather than just regional accents because the history and geography of Korea means they are very different and because Seoul dialect was made the ‘standard’. I can rarely hear the difference when I just hear people speaking either just like my Korean friends struggle to hear the difference between regional accents from the UK. further reading