Kaukritya

Kaukritya is a Buddhist term that is translated as "regret", "worry", etc. In the Theravada tradition, kukkucca is defined as worry or remorse after having done wrong; it has the characteristic of regret. In the Mahayana tradition, kaukritya is defined as sadness because of mental displeasure with a former action.
Kaukritya is identified as:

One of the fourteen unwholesome mental factors within the Theravada Abhidharma teachings
One of the four changeable mental factors within the Mahayana Abhidharma teachings
One of the five hindrances to meditation

Explanations

Theravada

Bhikkhu Bodhi explains:
The Atthasālinī gives the following definition of kukkucca:
Nina van Gorkom explains:

Mahayana

The Abhidharma-samuccaya states:
Mipham Rinpoche states:
Alexander Berzin explains: