A subindustry is a smaller part of a bigger industry, like how making car parts is a subindustry of the car industry.
Subindustries are important because they help make bigger industries work better.
Examples:
The subindustry makes the parts for the cars.
The toy-making subindustry is very busy.
The subindustry is a small part of the big industry.
The subindustry is like a baby industry.
The subindustry is the heart of the big industry.
The subindustry is like a little brother to the big industry.