What is the difference between ocean liner and cruise ship?

Cruise ships are mainly for get aways and touring the ocean. Ocean liners are large, longer ships that carry people across the ocean as a means of transport from one port to another. (Ex. Titanic was an ocean liner because it's purpose was the Trans-Atlantic route, which is the route from UK to US and back. People who don't know what they are talking about say Titanic was a cruise ship which is entirely false.