In simple words:

Abhinivesh means “very strong attachment or clinging”, especially:

• deep clinging to the body and life,
• fear of death or of losing what we have,
• not being ready to leave things, even when we know they are temporary.

In Jain dharma, such abhinivesh is a form of moha (delusion/attachment). Because of this clinging:

• the soul remains in saṁsār (birth–death cycle),
• we feel fear, worry and suffering,
• it becomes harder to follow the path of detachment (vairāgya) and right vision (samyak darshan).

So, Abhinivesh = strong clinging / fear of losing life and things, which binds the soul.