Many times I saw the phrase something 101, such as Microsoft Excel 101. What exactly does it mean?
closed as general reference by RegDwigнt♦ Jun 6 '12 at 10:07
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It means "introductory something". The allusion is to a college course with the course code 101, which in the American system and probably others indicates an introductory course, often with no prerequisites.
(chiefly US, postpositive) Basic, beginner, starting from scratch.
Geology 101 tells us that you can't build a reservoir on sandstone.
101 is the lowest course number, there's no 'zeroth' level. If someone attends a 220 course, they probably had 101 and 201 first.
In universities courses are (usually) marked by numbers, since they are hard to remember by name. First number corresponds to study year this course should be taken in, followed by 2 (or 3) course id. Usually the same subject course has greater id if they have to be taken in the same year. Therefore lower ids are usually assigned to basic courses. So, most basic course would be 101 then as the first 1 is for the 1st year & 01 is first the 1st course.