A startup is a new organizational unit created to solve a certain problem, startups are almost always reaching for the international user base, if its local and has a very limited number of potential users or market reach then it is an online business, but not a real startup. The term startup was used before as a start-up for starting a new venture, a new business activity, such as a restaurant, coffee shop or anything that is new.
During the .com era, it was called an online business.
During that time a new term came into use, a technology startup, so a new business that is either creating a new technology (like Google or Facebook) or has found a new use for an existing technology (like Uber or Airbnb). As time progressed, and people being people who love shortening things, technology start-up became tech startup, then because of I assume sheer laziness and love for shortening things, just startup (one word, new meaning). Since it was a widely use an overused and also misused word, technology start-up became a startup, no Hyphen ( - ) in the middle anymore.
Now as it always is, there are many that are lagging behind others, in this case the great many people who still do not know and understand what startup means, or worse, those who are convinced they do since they heard the word long ago when it had a different meaning, the original term for starting a new (any kind of) business. Those are the people who still do not understand the difference between a startup and an SME (small and medium enterprise). There is an evolution of how we use words and how the meaning of a word can change over time. A modern definition of a startup, there are a few that are generally agreed upon, but there no one all-encompassing definition of a startup, so I suggest to look up the definitions of a startup at Quora.
What are Scaleups...?
Scaleup is basically a startup that did not fail or stagnate but is instead succeeding and growing.