Popular standards are, according to Webster, "something established as a rule or basis of comparison in measuring or judging quantity, quality, value, etc.; a usage or practice that is generally accepted or followed; criterion; a piece of music that has remained popular for many years; suitable to speech or writing that is more or less formal; not slang, dialectal, obsolete." Popular standards from Tin Pan Alley are all of those things.
A standard is a song immediately recognized. It is a song one may not know the title to, but with the first four words and two measures, immediately sings along with (for example Irving Berlin's "Cheek To Cheek" is recognizable for the phrase "Heaven...I'm in Heaven...").
The standards from Tin Pan Alley are individual, written without the context of a script or storyboard, from a single inspiration. While many standards were later included in Broadway shows or Hollywood musicals, the songs were not written for that purpose.
The words and music reflect the creative personality of the songwriters and many times, their personal recollections and emotions. Special to Tin Pan Alley because of their enduring popularity and constant rebirth, most Americans cannot remember a time when standards did not exist. Standards are timeless and embedded in the American psyche-reflecting the soundtrack of our lives.
Never before and never after Tin Pan Alley was American popular culture so clearly defined by American popular music. Tin Pan Alley was based on the songwriter and the creation of standards. The collaborations that came out of Tin Pan Alley were unlike any the music world had ever known or would ever know again.