Full form of SMB is Small and Medium Business

Companies are classified as either Small or Medium-sized based on a threshold for the number of employees and annual turnover. In the US, a Medium-sized business has fewer than 500 employees and has annual sales below USD 100 Million. Similarly, in India, a small-sized business is one which has investment <= INR 100 Million (10 Cr) and annual turnover <= INR 500 Million (50 Cr), while a medium-sized business is one which has investment <= INR 500 Million (50 Cr) and turnover <= INR 2500 Million (250 Cr). For further country/region-specific categorization, refer to Wikipedia.