According to Steve Blank definition of a start-up is “a startup is a temporary organization used to search for a repeatable and scalable business model.”
What we understand from this is that, a startup is a temporary setup which requires a lot of repeated efforts to be made into a big, scalable business model. Once it is scaled it becomes a small size business with permanent business model.
Startups generally aim at providing disruptive innovations for a problem being faced. Many people look at startups as a company designed to grow fast.
Steve Blank classifies startups into six types as follows:
1. The Lifestyle startup
2. Small business startup
3. Scalable startup
4. Buyable startup
5. Large company startup
6. Social startup
https://www.feedough.com/what-is-startup/ will help you understand what is a startup better.