王八 literally means 'softshell turtle', but in everyday language it carries strong slang meanings — calling someone 王八 implies they are a cuckold or a despicable person (similar to 'bastard' or 'son of a bitch' in English). The insult often appears in the compound 王八蛋. The historical sense 'brothel owner' is archaic and rarely used. Be careful: this is a strong insult in Chinese, much stronger than 'turtle' in English.