OSI stands for Open Source Initiative, is an organization dedicated to cause of promoting open source software.
Bruce Perens and Erics Raymond were the founders of OSI, that was founded in Feb. 1998
OSI specifies the criteria for open source software and properly defines the terms and specifications of open source software.
Open source does not just mean access to the source code. The distribution terms of open source software must comply with the Open Source Definition by OSI.