Short answer: In Jainism, masturbation is not regarded as appropriate. Jain ethics center on brahmacharya (celibacy/self-control of sexual energy).

• For lay followers (householders): Brahmacharya means cultivating fidelity and self-restraint, usually keeping sexual relations within marriage and avoiding lustful acts or gratification beyond stewardship of senses. Masturbation is generally considered to be inconsistent with this ideal.
• For ascetics (monks/nuns): Complete celibacy is required, so any sexual activity, including masturbation, is avoided.

If you’d like a precise Jain-source explanation in the traditional terms (including notes on how Digambar and Śvetāmbara interpretations differ), you can read more here .