A caravan is a Persian word that refers to a group of people travelling together, often on a trade expedition (source: Wikipedia)... 

In STWALT, however, the caravan you get are in the tavern that offers to bring you to CASTLE for 50 golds and another encounter  with a merchant caravan, which you do deals and trading. 

Sometimes on your adventures, you might also encounter some destroyed caravans, which if you track them successfully leads you to an Orc Warband (orcs with 13 attack and random hp). You can loot destroyed caravans, but with a chance of being accused as an attacker (gain Criminality status).