Repentence is often mentioned in Mahayana texts. Outside of my knowledge of the meaning of the English word, which is colored by Christian concerns, I'm not sure what's involved. What is done during repentance? Is it just a matter of feeling sorry?
In Chinese Buddhism, repentance has two elements. The first:
One involves the rituals of confession in which we make offerings such as flowers and fruits to the Three Jewels as we sincerely confess and repent our sins. Through these rituals, we look honestly into our minds for the causes of our wrongdoings, sincerely accept responsibility for the harms we have caused, and resolve never to commit the same transgressions again.
And the second:
The other involves contemplation in which we reflect on the empty nature of all worldly phenomena, including our body, mind, and karma. When we keep our minds pure, clear, undisturbed by any thoughts, emotions and concepts, we will be able to transcend all karmic obstacles.
The formal process of repentance is achieved through the 88 Buddhas Repentance Ceremony:
In the 88 Buddhas Repentance Ceremony, participants repent by chanting the names of 88 buddhas, which is an excellent way to clear our karmic obstacles and draw out our inner wisdom. ... The power of chanting the buddhas’ names is documented in the past life story of Shakyamuni Buddha at the time of the Buddha Suryarasmi. One day, Shakyamuni Buddha, a practicing monk, heard the chanting of the 53 buddhas’ names and immediately sensed an indescribable joy, which he felt must be shared with all beings. He had the message passed along to 3,000 people, who followed his example and chanted the 53 buddhas’ names with deep respect and remembered each buddha’s name by heart. These people subsequently attained buddhahood in three different time periods, or kalpas.
Shakyamuni Buddha also felt the suffering of beings who had to carry with them heavy karmic obstacles, so he taught them to repent by chanting the 35 buddhas’ names.
Here's a video of the ceremony itself:
Platform sutra describes 'non-symbolic repentance' as including sincere promise to never repeat faults in the future, and acknowledgement of our past faults, that are caused by defilements of mind (ignorance, pride, and envy), which we decide to clean off our thoughts for good.