Small and Medium-sized Enterprises
Companies whose headcount or turnover falls below certain limits.
For example, the European Union takes SMEs as having fewer than 250 employees and either turnover not exceeding €50m or (annual) balance sheet not exceeding €43m. Even within the EU, Member States may use different levels for domestic purposes.
The term uses 'enterprises' and not 'companies'. Of course, it might have used 'firms' or 'businesses' and so on rather than 'enterprises'. The reason is that the overwhelming majority of enterprises are not companies but are unincorporated small businesses.