The letter [M] at the back of the title is the abbreviation of the English word "monograph", which means monograph. The types of references (that is, citations) are identified by a single letter, so [M] means that the book belongs to a special work (studied and discussed in a certain aspect).
[M] This logo is used in papers and is an important part of the standard format of references. Usually there will be such a sign at the end of the book.
Extended data:
[M] is a file type identifier. In addition to [M], there are other commonly used document types, such as:
(1) periodical [J] (periodical), (2) monograph [m](3) collection of essays [C] (collection of essays), (4) dissertation [d](5) patent [P] (patent).
In addition to the commonly used literature types, there are also electronic literature types. The type of electronic document is identified by two letters, such as:
(1) magnetic tape (MT), (2) magnetic disk (DK), (3) compact disk (CD-ROM), (4) online network (OL) (online) and so on.
References:
Document Type Recognition _ Baidu Encyclopedia