Modernization is a term that is used to differentiate between societies with traditional economies and social structures and those whose economies and social structures have changed significantly. The latter are said to have modernized. Traditional societies are based on agriculture and are socially fairly static. Modern societies are based on industry and are socially dynamic and complex.
Economically, the difference between traditional and modern societies is fairly clear. Traditional societies have economies that are based on agriculture. Modern societies have diversified beyond this. They have come to have economies based on industry.
The social differences between modern and traditional societies are more complex. Basically, traditional societies were very hierarchical. Their structure tended to be pyramidal with a very small elite at the top that exerted top-down authority on the lower levels of society. Such societies were static with no change expected. Industrialization changed this. It created a society that was much more horizontal. There is much less hierarchy. There is also the expectation that change is going to be relatively continual. These societies become more and more complex over time.
Thus, modern society is industrial, more egalitarian, and more complex than traditional society.