Actually only 3,
there are activities that are illegal, a Law specifically states what the activities that are illegal are has been written by government.

then there are activities that have laws specifically stating they are legal only in said circumstances Legalization, made legal by laws which usually also regulate the activity.

Third decriminalization, remove existing laws making it illegal without writing new laws making it legal only under the rule of the law. most of our personal activities fall in this category no government rule is needed to make them legal or illegal. We don't need a law to make any kind of sex legal, we just need to get the government out of our business making certain kinds of sex illegal, unless it truly hurts a portion of the population like rape, or underage sex by adults. The anti traffickers would be better served working on laws to go after any kind of trafficking regardless of activity and leave the sex issue out of it altogether.

most proposals for legalization call for various regulations, i.e. id cards, med checkups, sometimes eros zones etc, where as decriminalization proposals say just leave the occupation alone and let people have sex for pay with so strings attached. This is not  new concept but applies to bringing an illegal activity into being a legal activity. When prohibition was lifted a series of laws and regulations were attached to protect the public and tax the product. The state always likes to attach regulations and taxes. The concept of freedom is to be unbound. The interests of society bring questions of safety and protection into the discussion. Different pokes for different folks....