The Union Public Service Commission (UPSC) is a constitutional body in India responsible for conducting various prestigious civil service examinations at the national level. UPSC exams are highly competitive and serve as a gateway to a wide range of administrative, diplomatic, and public service positions in the country. In this detailed explanation, I will provide an overview of the different UPSC exams, their eligibility criteria, exam patterns, and stages involved. Please note that the response will be shortened to fit the word limit.

Civil Services Examination (CSE)

• Eligibility: Bachelor's degree in any discipline from a recognized university.
• Stages: Preliminary Examination (Objective), Main Examination (Written), Interview (Personality Test).
• Subjects: General Studies (GS), Optional Subject (chosen by the candidate).
• Optional Subjects: Candidates can choose one optional subject from a list provided by the UPSC.
• Services: Indian Administrative Service (IAS), Indian Foreign Service (IFS), Indian Police Service (IPS), and other central services.

Indian Forest Service Examination (IFoS)

• Eligibility: Bachelor's degree in one of the following subjects: Animal Husbandry and Veterinary Science, Botany, Chemistry, Geology, Mathematics, Physics, Statistics, or Zoology.
• Stages: Preliminary Examination (Objective), Main Examination (Written), Interview (Personality Test).
• Subjects: General Studies (GS), Optional Subject (chosen by the candidate).
• Optional Subjects: Same as CSE, with the addition of Forestry as an optional subject.
• Services: Indian Forest Service (IFS).

Engineering Services Examination (ESE)

• Eligibility: Bachelor's degree in Engineering from a recognized university.
• Stages: Preliminary Examination (Objective), Main Examination (Conventional/Written), Personality Test (Interview).
• Subjects: General Studies and Engineering Discipline (chosen by the candidate).
• Services: Indian Engineering Services (IES).

Combined Medical Services Examination (CMS)

• Eligibility: MBBS degree from a recognized university.
• Stages: Written Examination, Personality Test (Interview).
• Services: Medical Officer positions in various government organizations.

National Defence Academy Examination (NDA)

• Eligibility: 10+2 or equivalent examination pass.
• Stages: Written Examination, Interview by the Services Selection Board (SSB).
• Services: Army, Navy, and Air Force wings of the NDA.

Naval Academy Examination

• Eligibility: 10+2 or equivalent examination pass with Physics and Mathematics.
• Stages: Written Examination, Interview by the Services Selection Board (SSB).
• Services: Indian Navy.

Combined Defence Services Examination (CDS)

• Eligibility: Bachelor's degree for Indian Military Academy and Officers' Training Academy, and graduation or engineering degree for Air Force Academy and Naval Academy.
• Stages: Written Examination, Interview by the Services Selection Board (SSB).
• Services: Indian Military Academy (IMA), Indian Naval Academy (INA), Air Force Academy (AFA), and Officers' Training Academy (OTA).

Central Armed Police Forces Examination (CAPF)

• Eligibility: Bachelor's degree from a recognized university.
• Stages: Written Examination, Physical Standards/Physical Efficiency Tests, Medical Standards Tests, and Interview/Personality Test.
• Services: Assistant Commandant positions in various Central Armed Police Forces.

Combined Geo-Scientist and Geologist Examination

• Eligibility: Master's degree in Geology/Applied Geology/Marine Geology/Mineral Exploration/Earth Science and equivalent subjects.
• Stages: Written Examination (Objective/Descriptive), Interview/Personality Test.
• Services: Geological Survey of India and Central Ground Water Board positions.

These are the major UPSC examinations in India. Each exam follows a specific pattern and syllabus. Candidates are advised to refer to the official UPSC website and notifications for detailed information regarding eligibility, application procedures, and syllabus for each examination.