Jain is not a caste.

• Jain is a dharma (religion), like Hindu, Muslim, Sikh, etc.
• People who follow Jain dharma are called Jains.
• Jains can belong to many different social communities (jatis) like Oswal, Porwal, Agarwal, Khandelwal, Srimal, Vania, etc. These are community or caste names, not the religion itself. ( jainknowledge.com)

In Jainism:

• Spiritual progress does not depend on caste or birth.
• Any soul from any background can follow Jain dharma and attain moksha through right faith, right knowledge and right conduct. ( jainknowledge.com)

So: Jains are followers of Jain religion, not a single caste.

You can read a simple explanation here