Industrialization (or Industrialisation) is a process that happens in countries when they start to use machines to do work that was once done by people. Industrialization changes the society as it happens. During the industrialisation of a country people leave farming work to take higher paid jobs in factories in towns.
Industrialization is part of a process where people adopt easier and cheaper ways to make things. Using better technology, it becomes possible to produce more goods in a shorter amount of time. A single person can produce more things.
After industrialization people also do more specialized jobs. For example before industrialization, a cobbler made the whole shoe. He worked on one pair of shoes, finished that, and then did the next pair of shoes. With industrialization, there are many people involved in making shoes. An individual shoemaker has a smaller task, however. There is one person that cuts the sole of the shoe. Another person stitches it on. In short there is division of labour. The machines to make the shoes cost a lot of money so the factory will be owned by a rich person who can afford the machines.
Industrialization started in England with the industrial revolution in the 18th century. It spread first to parts of Europe, and to North America. In the 20th century industrialization spread to most other countries.