Historical graphies were oscillating between the voiced -s- and the unvoiced -ss-: Oson (1441), Osom, Osson, Ozon (1538), le Lozon (1581), l'Ouson (1585).

[4] The valley of the Ouzoum is separated in two distinct parts by a 9-kilometre (6 mi) long narrow pass.

The villages in the upper part of the valley (Arbéost and Ferrières) belong to the Hautes-Pyrénées and have relationships with the Val d'Azun, on the other side of the mountain.

On the other hand, the lower part of the valley, close to Pau, is Béarnese (Pyrénées-Atlantiques).

After the basin of Ferrières, the Ouzoum flows through a narrow pass bordered by steep limestone slopes.