Small and Medium Enterprises or SME is a term usually used to stands for all business with the following attributes (ref. Tanzania SME Policy)
Staff size of less than 100 or
Turnover of less than TZS. 800m
The policy further describe SME in a more detailed form
Micro enterprise is businesses with less than 5 employees and operates with a turnover of less than TZS. 5M. The Small Enterprises are business with staffs between 5 to 49 and operating with a turnover between TZS. 5M to 200M. The Medium Enterprises operates with employees between 50 to 99 and has a turn over capital between TZS. 200m to TZS. 800m.
These factors vary country to country due to differing in living standards. It also varies within the country as defined by different institutions like banks have their own definition, government, international organizations etc.