popular adj.

c. 1300, peple, "humans, persons in general, men and women," from Anglo-French peple, people, Old French pople, peupel "people, population, crowd; mankind, humanity," from Latin populus "a people, nation; body of citizens; a multitude, crowd, throng," a word of unknown origin. Based on Italic cognates and derivatives such as populari "to lay waste, ravage, plunder, pillage," Populonia, a surname of Juno, literally "she who protects against devastation," the Proto-Italic root is said to mean "army" [de Vaan]. An Etruscan origin also has been proposed. The Latin word also is the source of Spanish pueblo, Italian popolo. In English, it displaced native folk.

Sense of "Some unspecified persons" is from c. 1300. Meaning "body of persons comprising a community" is by mid-14c. (late 13c. in Anglo-French); the meaning "common people, masses" (as distinguished from the nobility) is from late 13c. The meaning "members of one's family, tribe, or clan" is from late 14c.

The word was adopted after c. 1920 by Communist totalitarian states, according to their opponents to give a spurious sense of populism to their governments. It is based on the political sense of the word, "the whole body of enfranchised citizens (considered as the sovereign source of government power," attested from 1640s. This also is the sense in the legal phrase The People vs., in U.S. cases of prosecution under certain laws (1801).

The people are the only censors of their governors: and even their errors will tend to keep these to the true principles of their institution. To punish these errors too severely would be to suppress the only safeguard of the public liberty. The way to prevent these irregular interpositions of the people is to give them full information of their affairs thro’ the channel of the public papers, and to contrive that those papers should penetrate the whole mass of the people. [Jefferson to Edward Carrington, Jan. 16, 1787]

People of the Book "those whose religion entails adherence to a book of divine revelation" (1834) translates Arabic Ahl al-Kitab. 

"having popular appeal," 1926, of individual songs from many genres; 1954 as a noun, as genre of its own; abbreviation of popular; earlier as a shortened form of popular concert (1862), and often in the plural form pops. Pop art is recorded from 1957, said to have been in use conversationally among Independent group of artists from late 1954. Pop culture attested from 1958, short for popular culture (which is attested by 1846).

To dismiss him [Johnnie Ray] out of hand one would have to share (as I can't) that facile contempt for "pop" culture, and by implication "pop" audiences, which is the principal flaw of that ambitious new musical, "Expresso Bongo." [Kenneth Tynan, "At the Theatre," The Observer, May 11, 1958]