Mahendra Singh Dhoni made his ODI (One Day International) debut in Chittagong.

Explanation:
Mahendra Singh Dhoni, popularly known as MS Dhoni, is a former Indian cricketer and one of the most successful captains in the history of Indian cricket. He made his ODI debut against Bangladesh on December 23, 2004, in Chittagong.

Here is a detailed explanation of the answer:

1. Mahendra Singh Dhoni: Start by introducing Mahendra Singh Dhoni and his significance in Indian cricket. Mention that he is a former Indian cricketer and one of the most successful captains in the history of Indian cricket. Talk about his achievements and contributions to the Indian cricket team.

2. ODI Debut: Explain what ODI debut means and its significance in a cricketer's career. Mention that ODI is a limited-overs format of cricket where each team gets to play 50 overs. Emphasize that making an ODI debut is an important milestone for any cricketer.

3. Date and Location: Provide the specific details of Mahendra Singh Dhoni's ODI debut. Mention that he made his ODI debut on December 23, 2004. State that the match was held in Chittagong, Bangladesh. Explain that Chittagong is a major city in Bangladesh and also a cricketing venue.

4. Opponent: Mention that Bangladesh was the opponent team for Dhoni's ODI debut. Talk about the significance of playing against Bangladesh, which was still a developing cricketing nation at that time.

In summary, Mahendra Singh Dhoni made his ODI debut against Bangladesh on December 23, 2004, in Chittagong. It was a significant moment in his career as he went on to become one of the most successful cricketers and captains in Indian cricket history.