The most common meaning for "IAB" is Internet Architecture Board, previously known as the Internet Activities Board. This is both an advisory body for the Internet Society and a committee of the Internet Engineering Task Force.
The IAB consists of 13 members, six of whom are nominated every other year by the Internet Engineering Task Force. The committee focuses on pertinent Internet issues via teleconference twice a month and in person three times a year. Some of the topics discussed include the future of Internet addressing, partial check sums for UDP traffic, network management, service identifiers and filtering. The main focus is to describe principles that are necessary to maintain or improve Internet functions.