Background: George Jacob Gershwin (; September 26, 1898 -  July 11, 1937) was an American composer and pianist. Gershwin's compositions spanned both popular and classical genres, and his most popular melodies are widely known. Among his best-known works are the orchestral compositions Rhapsody in Blue (1924) and An American in Paris (1928), as well as the contemporary opera Porgy and Bess (1935).
Context: In 1913, Gershwin left school at the age of 15 and found his first job as a "song plugger". His employer was Jerome H. Remick and Company, a Detroit-based publishing firm with a branch office on New York City's Tin Pan Alley, and he earned $15 a week.  His first published song was "When You Want 'Em, You Can't Get 'Em, When You've Got 'Em, You Don't Want 'Em" in 1916 when Gershwin was only 17 years old. It earned him 50 cents.  In 1916, Gershwin started working for Aeolian Company and Standard Music Rolls in New York, recording and arranging. He produced dozens, if not hundreds, of rolls under his own and assumed names (pseudonyms attributed to Gershwin include Fred Murtha and Bert Wynn). He also recorded rolls of his own compositions for the Duo-Art and Welte-Mignon reproducing pianos. As well as recording piano rolls, Gershwin made a brief foray into vaudeville, accompanying both Nora Bayes and Louise Dresser on the piano. His 1917 novelty ragtime, "Rialto Ripples", was a commercial success.  In 1919 he scored his first big national hit with his song, "Swanee", with words by Irving Caesar. Al Jolson, a famous Broadway singer of the day, heard Gershwin perform "Swanee" at a party and decided to sing it in one of his shows.  In the late 1910s, Gershwin met songwriter and music director William Daly. The two collaborated on the Broadway musicals Piccadilly to Broadway (1920) and For Goodness' Sake (1922), and jointly composed the score for Our Nell (1923). This was the beginning of a long friendship. Daly was a frequent arranger, orchestrator and conductor of Gershwin's music, and Gershwin periodically turned to him for musical advice.
Question: what is plugger

Answer:
His first published song was "When You Want 'Em, You Can't Get 'Em, When You've Got 'Em, You Don't Want 'Em" in 1916 when Gershwin was only 17 years old.