The graph expresses the annual evolution of the frequency of use of the word Â«bogginessÂ» during the past 500 years. Its implementation is based on analysing how often the term Â«bogginessÂ» appears in digitalised printed sources in English between the year 1500 and the present day.
charm (countable and uncountable, plural charms) 1  An object, act or words believed to have magic power (usually carries a positive connotation). a charm against evil. 2  The ability to persuade, delight or arouse admiration; often constructed in the plural. He had great personal charm.
I believe that Lehman Engel's term of charm song describes a song that is there merely to charm an audience, and is not necessarily plot or character driven. Here I Am introduces a major character late in Act One in a big way, so I think it is much more than a charm song.