unixODBC is an open source project that implements the ODBC API on non windows platforms.
ODBC is an open specification for providing application developers with a predictable API with which to access data sources.
The ODBC API was outlined by X/Open and ISO, and it is available on all major platforms. Microsoft platforms include many enhancements to this specification.
unixODBC is an open source project that implements the ODBC API (including all the enhancements made by Microsoft) on non windows platforms.