The pin area is a part of the data cache where data from tables with caching mode Keep is held, see Caching Mode.
You configure the size of the pin area using the support database parameter DataCachePinAreaThreshold. For Multiple Client One Database (MCOD) systems the support database parameter EnableLivecachePinArea should be set to YES.
Concepts of the Database System, Working Memory Areas
Database Administration, Support Database Parameters, Creating Tables
SQL Reference Manual, CREATE TABLE Statement