What is the definition of tourism?
I start this post saying that this is not an academic article and doesn't have any academic objective. It's, also, an abstract that has the purpose to explain, in an easy way, what is tourism for those who don't work with it, for those who are not inlvolved with it or for those who wants to learn more about it.
To understand Tourism, we need to learn where it fits into our lives, and fot that, we'll use the Maslow's Hierarchy of Needs, created in the fifty's decade. Maslow was a north american psychologist considered of great importance in the area of administration. In his theory, he shows the human being needs and divide them in relevance's categories. The first two lines are the essential needs to survivance bases, and that means that we can't live without them. The fisrt line is where the physiological needs are (breath, eat, sleep, etc.). The second line is where the security needs are, this means that we can't live always feeling like we are in danger. The third line are the social needs, the necessity we have to socialize with other people and have intimate relationships. The fourth line are the self-esteem/actualization needs (if you don't really believe in yourself, you can't truly live). And fifth line is the self-realization needs.

The execution of tourism is on the last line, the self-actualization one. Because it isn't a survival need, in fact, is a living need. Leaving it clearer, when we receive our paychecks we have a priority list (or, at least, we should've): First we buy food, pay the essencial bills (eletricity, house rent, etc), clothes, save for gas or bus, etc. Tourism will only be one line in this list if all the other matters have been paid. If we're hungry, or anything like that, we will not spend money with a trip.
Now that we understand where tourism is in our lives, we'll move on to its definition. To put a definition in something it's necessary, but it's also, to (de)limit it. Thus, to put lines and to delimit something can damage the comprehension of the whole. So, I hope to incite your curiosity and challenge you to search a bit more about this matter to understand it better.
The word "tourism" it's formed from the word tour, which is derived from Old English turian, from Old French torner, from Latin tornare; 'to turn on a lathe,' which is itself from Ancient Greek tornos 'lathe'.
Fuster (Teoría y técnica del turismo, 1971) explain that the word "tourist" was published for the first time in an English dictionary (The Shorter Oxford English Dictionary) in 1800. And its definition was: A person who does a tour or tours. The one who does it for recreation: Who does it for pleasure or because of his/her culture, visiting a number of places of his/her interests, scenary or similar."
One of the firsts printed definitions of tourisms was in the Manual Dictionary of Economics, Social Policy and Administration (Handwörterbuch der sweizerischen volkswirtschaft, sozialpolitik und verwaltung), in 1905, from the German author Eduard Guyer Freuler. In the dictionary, Freuler explains that tourism is a current phenomenon that explains itself by our constant need to rest and to be in different places, in new airs, to enter into relations with different peoples, the well-being that comes from being in contact with nature, and many other things.