GDAL is a large piece of software for working with geospatial data. GDAL consists of several parts: a portability library, a generic system of classes for raster and vector data, a mechanism of adding format drivers and an increasing set of drivers, an increasing set of implementations of geospatial algorithms, several command line tools, and a foreign function interface (FFI) with bindings for several languages. Geoinformatica links to GDAL through the GDAL Perl bindings, i.e., the Geo::GDAL set of modules.
Besides several libraries to which GDAL links because they are required for drivers, GDAL also links to two important geospatial libraries: Proj4 and GEOS.
The vector data part of GDAL is called OGR. Thus GDAL is sometimes referred to also as GDAL/OGR.