The word "calf" is mentioned 12 times in 10 verses in the Quran. And regarding your question, when Prophet Musa (AS) went to Mount Sinai to receive the commandments from Allah, his people became impatient and asked Prophet Harun (AS) to make a god for them to worship. Harun (AS) tried to convince them to stay on the right path, but eventually, they made a golden calf and started worshipping it. This incident is mentioned in several verses of the Quran, including Surah Al-A'raf and Surah Ta-Ha.