A scaleup company or just scaleup is defined by the OECD as a company having an average annualized return of at least 20% in the past 3 years and had at least 10 employees at the start of the 3-year period.

Scaleup businesses are distinct from startups in their stage of development. While startups are typically in the initial phases of establishing their market presence and business model, scaleups have moved beyond this stage and are focused on expanding their market share, revenue, and workforce at a rapid pace. Scaleups are considered critical to the UK economy due to their significant contribution to job creation, innovation, and economic growth. 

These businesses often face unique challenges compared to smaller startups or larger established companies. Challenges include managing rapid growth, scaling their operations effectively, attracting and retaining talent, and securing sufficient funding to fuel their expansion. The UK government and various business organizations offer support and resources to help scaleups overcome these challenges and sustain their growth trajectory.