What is the full form of "SMB"?

A small and medium business (SMB) is a business that, due to its size, has different IT requirements - and often faces different IT challenges - than do large enterprises, and whose IT resources (usually budget and staff) are often highly constrained.
For the purposes of its research, Gartner defines SMBs by the number of employees and annual revenue they have. The attribute used most often is number of employees; small businesses are usually defined as organizations with fewer than 100 employees; midsize enterprises are those organizations with 100 to 999 employees.