Definition of 101 in US English:
 101
adjective ˌwənˌōˈwənˌwənˌōˈwən
1postpositive Denoting an introductory course at college or university in the subject specified.
 Example sentencesExamples
-  The Saturday and Sunday 101 classes start at 3pm
 -  Signing up for a Stripper 101 class can be a real edge.
 
- 1.1informal  Denoting the elementary or basic facts associated with the field or subject specified.
 stuff that you should learn in hacking 101