what is JEE Main and JEE Advanced?

What are they?

JEE Main: A national-level entrance exam conducted twice a year (January and April sessions) for admission to various undergraduate engineering programs at NITs (National Institutes of Technology), IIITs (Indian Institutes of Information Technology), and other centrally funded technical institutions (CFTIs). It also serves as the qualifying exam for JEE Advanced.
JEE Advanced: The second stage of the IIT-JEE (Indian Institutes of Technology Joint Entrance Examination). It's conducted once a year by one of the IITs on a rotational basis. Only the top 2.5 lakh candidates from JEE Main are eligible to appear for JEE Advanced. Clearing this exam opens doors to the prestigious IITs, IISc (Indian Institute of Science), and some other top-tier institutions.

Key Differences

Purpose: JEE Main acts as a screening test for JEE Advanced, while JEE Advanced is the final exam for IIT admissions.
Conducted by: JEE Main is managed by the National Testing Agency (NTA), while JEE Advanced is organised by different IITs each year.
Frequency: JEE Main is held twice a year, while JEE Advanced is conducted only once.
Eligibility: Anyone who has completed 12th grade or equivalent can appear for JEE Main. Only the top 2.5 lakh JEE Main scorers are eligible for JEE Advanced.
Syllabus: While both exams cover Physics, Chemistry, and Mathematics, JEE Advanced has a slightly more extensive syllabus and questions are known to be more challenging and conceptual.
Exam Pattern: JEE Main has two papers (Paper 1 for B.E./B.Tech and Paper 2 for B.Arch/B.Planning) with objective-type questions. JEE Advanced has two papers (Paper 1 and Paper 2) with a mix of multiple-choice and numerical-type questions.
Difficulty: JEE Advanced is widely regarded as significantly more difficult than JEE Main.

In a nutshell:

JEE Main is the first step towards getting into NITs, IIITs, and other good engineering colleges.
JEE Advanced is the gateway to the IITs and is considered one of the toughest entrance exams in the world.

I hope this detailed explanation provides a clear understanding of JEE Main and JEE Advanced.