Ratri bhojan tyag means giving up eating food at night.

In Jain Dharma, this vow means:

• one should not consume food after sunset and before sunrise,
• because night eating increases himsa toward very small living beings,
• and it helps in practicing discipline, purity, and self-control.

Spiritual meaning

• to follow ahimsa,
• to reduce harm to living beings,
• to protect health and restraint,
• and to support a simple, disciplined Jain way of life.

In short

If you want, I can also explain its Jain scriptural importance in simple words.