If Startup is “an organization formed to search for a repeatable and scalable business model” [Steve Blank, https://steveblank.com/2010/01/25/whats-a-startup-first-principles/]
then a Scaleup is “an organization formed to establish the foundation, skills and systems to create, deliver and harvest value in order to capture sufficient market share to influence the market”.
(The definition of scaleup should put the emphasis on building the systems)
Inferred from Steve Blank’s post above: A Scaleup is the transitional stage between Startup and Company.