This o' is how people write of when they copy a relaxed spoken sound: of has worn down to a little o. You know it from o'clock (of the clock), and you see it in cup o' tea, will-o'-the-wisp, jack-o'-lantern. It is informal on purpose. In careful writing you would put of. It is not a new word; it is of in short clothes. You will also see o' in Irish family names such as O'Brien. That lookalike comes from Irish Ó and means ‘grandson of’ or ‘from the family of.’ Wiktionary treats that Irish o' as a different word, unrelated to this English o' for of.

（口語）的（of 的省略寫法，如 o'clock）