What does 101 means in a course title?

Many years ago(1929), for the first time a university in New York, United States, used a combination of numbers to describe its course numbers. The Oxford English Dictionary for the first time found this combination at 1929 in this university’s course catalog. But what does this combination really means?

In fact this combination is made of three different parts:

• First digit: Corresponded to the college year. Number 1 goes for freshmen, 2 for sophomores, 3 for juniors, 4 for seniors in under graduates and 5 or above for graduate courses
• Second digit: Corresponded to the particular subject or department
• Third digit: Corresponded to the sequence number within a series of courses on the same subject

Based of this arrangement, when you see a course like Learning C#.NET 101, it means that this course is for beginners, and it is the first part of the this course. next part of this course will have 102(lets pronounce it as “one-oh-two”) code and the next level of this course will be 201 etc.