"Pays d'Oc" is a protected geographical indication, it covers the south of France bordering the Mediterranean and the area west of the Rhône (in the southernmost section). The legal regulations for "Vin de Pay" (today IGP) apply, which are significantly less restrictive than those for the protected AOC appellations, especially with regard to the permitted grape varieties. Therefore, IGP wines are often (or even mostly) made from grape varieties that are not permitted as AOC (Appellation d'Origine Contrôlée - internatonal: PDO - Protected Designation of Origin) in the corresponding area.
Complicated? Hardly understandable for the average consumer. At best, he understands: This wine comes from the south of France, from Pays d'Oc. Those who are more familiar with the region and the French wine law also know that Colombiers (a small town near Béziers) is not located in one of the traditional AOC appellations (PDO) and is therefore marketed under the Pays d'Oc designation of origin.