I try just to use standard definition. A startup as most people use the word means a comparatively small, comparatively young company that is designed to grow very big. Most but not all such companies create technology, because technology scales so well.

Basically, the difference between a small business and a startup is like the difference between a shrub and a redwood seedling.

The metaphor isn't perfect, because occasionally companies are transformed from one to the other. But this is extraordinarily rare.