In Jainism, karma means subtle matter that binds to the soul as a consequence of every intentional action, including thoughts, speech, and body. Casual sex binds karma because itāpplies strong passions (kama, lust, attachment) and causes harm to living beings, which creates negative karmic particles.

Key ideas in simple terms:

• Karma is shaped by intention and attachment. Casual sexual behavior often arises from and reinforces desires (kama) and the illusion of looking for happiness outside proper conduct.
• Such acts can involve deceit, coercion, or commodification, which cause harm or violence to others. These harms bind karma to the soul.
• The binding of karma affects future births, life conditions, and spiritual progress. More binding and heavier karma make liberation (moksha) harder.

In Jain ethics, the emphasis is on controlling inner passions and acting with non-violence (ahimsa), truth (satya), and self-control. For lay followers, this includes practicing chastity within appropriate contexts and cultivating restraint, so as not to create unnecessary karmic burden. For monks and nuns, celibacy is a central vow to prevent karma from binding.

Note: Jain traditions discuss the mechanisms of karma (adhi-ashraya, aghatiya/ghatiya karmas, etc.) in nuanced ways. The above captures the core ethical idea: sexual conduct driven by uncontrolled passion tends to generate negative karma because it harms self and others and weakens spiritual progress.