We seem to have come to use the terms cruise ship and cruise liner as synonymous these days but that is not what they started life out as.
A cruise ship is basically one which provides a journey for pleasure. It is a whole experience where the on-board daily activities and the evening dining and entertainment form a major part of the pleasure.
Their focus is to depart from a port, travel around a specified region, as in Western Mediterranean cruises, and then return to that same port for disembarkation. The bit in the middle is what people go on them for.
Traditionally liners have served a different purpose in that the people traveling on them were using them to get from one place to another. An example being the ocean liners that transported passengers between London and New York.
These transoceanic liners had to be constructed to a much higher specification. The Atlantic ocean can get very choppy so they needed a lot of protection from the rough seas. They needed more fuel and had to carry sufficient food and drink for the whole journey whereas the cruise ships can collect fuel and supplies from any port that they stop at.
They also tended to be very lavish as the only people who could travel on them were wealthy and expected luxury.
By their nature they had an extremely high fuel consumption, they had a much deeper draught and their decks were more about withstanding the weather conditions than lying around sunbathing. These points meant that they were limited in which ports they could enter so were not suitable for something like an island hopping Caribbean cruise.
The cruise ships of today have to be built with tourists who like lying in the sun and want to be entertained at any other time. Consequently, most do not normally cross oceans and their main journeys are in tranquil seas where there is a lot of sunshine.
It is true to say that there has been a blurring in the terminology but the construction restrictions still do apply. There are still some vessels that can adapt to both sets of conditions. These are the ones we sail on when doing a world cruise perhaps which will also take a lot longer to return back to the port of origin than a normal cruise.
MS Mona Lisa and MS Marco Polo are two examples of oceans liners that have adapted. Whereas there used to be a few, the Queen Mary 2, operated by Cunard, is only liner now dedicated to the transatlantic trip. Most passengers nowadays, use it as a vacation trip though rather than a way of getting from one place to another.
In the recent past few years cruising has become a more and more lucrative industry with several new ships being built annually to satisfy the demand. We have moved a long way from the way it used to be but I hope that the differences between cruise liners and cruise ships will be remembered for ever.