According to Ibn Battuta, a Moroccan traveller to India during the Delhi Sultanate, the method of postal system in which the royal horses were used to transfer packages, is called:

The correct option is Uluq.

Explanation:

Ibn Battuta, a famous Moroccan traveler who visited India during the reign of Sultan Muhammad bin Tughluq in the 14th century, provided a detailed description of the efficient postal system established during the Delhi Sultanate.

According to his travelogue (Rihla), the postal system (known as Barid) was divided into two types:

1. Uluq: The horse-post system. In this method, royal horses stationed at a distance of every four miles were used to transfer messages, news, and packages quickly across long distances.

2. Dawa: The foot-post system. This method relied on runners stationed every third of a mile, who carried rods with copper bells to signal their arrival and quickly hand over parcels or dispatches to the next runner.

Therefore, the horse-based postal system was specifically called Uluq.