What does the "m" in the reference stand for?

1 periodical author. Title [J] Title, year of publication, volume (issue): page number \x0d\2 monograph author. Title [m]. Version (first edition not recorded). Place of publication: publisher, year of publication. Page number \x0d\3 Author. Title. 4. Author of dissertation. Title [D] Storage location: storage unit, year \x0d\5. Title of patent document. Country, patent number. Publication date \x0d\6. Standard number, standard name \x0d\ 7. Newspaper writer. Title. Name and patent number of newspaper. 8 Report author. Title [r]. Save location: year \x0d\9 electronic document author. Title [Electronic document and carrier type identification]. Document source, date \x0d\ 2. Document type and its identification \x0d\ 1. According to GB3469, ① periodical [J] ② monograph [M] ③ thesis [C] ④ dissertation [D] ⑤ patent [P] ⑤ standard [S] ⑦ newspaper [N] ⑧ technical report [R] 2. The carrier type of electronic documents is identified by two letters. For example: ① magnetic tape [MT] ② disk [DK] ③ optical disk [CD] ④ online network [OL] 3. The method of identifying the reference type of electronic document carrier type is [document type identification/carrier type identification]. For example: ① Online online database [DB/OL] ② Tape database [DB/MT] ③ CD-ROM books [M/CD] ④ Disk software [CP/DK] ⑤ Online periodicals [J/OL] ⑤ Online electronic bulletin [EB/OL].