The 4th vrat in Jainism is Brahmacharya — celibacy / chastity / control of sensual desires.

Meaning:

• avoiding sexual indulgence
• maintaining purity in thoughts, words, and actions
• practicing self-control over desires

In Jain ethics:

• For munis/sadhus, brahmacharya is observed fully and strictly as one of the five Mahavratas.
• For shrावaks/shrāvikās (lay followers), it is observed as a vow of restraint within the five anuvratas.

Simple order of Jain vows:

1. Ahimsa – non-violence
2. Satya – truth
3. Asteya – non-stealing
4. Brahmacharya – celibacy / chastity
5. Aparigraha – non-possessiveness

If you want, I can also give the 5 vows in Gujarati/Hindi/Sanskrit form.