What online gambling is legal?

Could you please elaborate on the legality of online gambling? Is there a general rule that applies to all countries, or does it vary depending on the jurisdiction? Are there specific types of online gambling activities that are generally considered legal, such as sports betting or casino games? Are there any particular regulations or licenses that gambling operators need to obtain in order to operate legally? Lastly, are there any countries that have banned online gambling altogether? Thank you for your time.