According to the Merriam-Webster Dictionary, a nomad is «a member of a people who have no fixed residence but move from place to place usually seasonally and within a well-defined territory». This concept applies, for example, to Bedouins, people that live in the desert, and Mongolians. The main reason why they move from place to place is because they herd animals (especially camels, in the case of Bedouins, and horses, in the case of Mongolians).
Nomads should not be confused with the merchants that used to cross the desert with goods to be sold on the other side. These caravans were very popular in the old days of the silk route and also in the Sahara Desert (think about the typical image of camels in line, full of goods attached to their back). While caravan merchants would go from one city to another, nomads would stay in the same place for a certain period of time, living in tents in the meantime.
Digital nomads modernised this concept. They too move from place to place and stay there for a certain period of time. However, instead of herding animals, they use technology to work remotely. And they do not usually live in tents, but in rented houses, although there are no rules in this respect. In fact, there are those who buy a camper van (brand new or an old one that they rebuild as they please) and literally move their house around.
The concept somehow expanded to also mean someone who roams without a purpose or a destination. However, this is different from a vagabond. A vagabond is someone who has no money, no professional occupation, and no place to live (they usually live on the street). Nomads have money and a profession, thus, they can pay for accommodation and supplies.
Being a nomad is not for everyone… but, then again, being in the same place doing the same things with the same people is not for everyone either. Before technology, people did not have much choice. If you were born into a nomad family, you would become a nomad, and if you were born, let’s say, in a farm, you would become a farmer. Of course, throughout the centuries, there were always rebels, people who did not accept their fate and would find a way to do what they really wanted (artists, mostly). However, nowadays, with new technology and the Internet, it gets easier to choose what you want to become. This does not mean that it is easy or without difficulties, for sure.