The song talks about working-class people being the ones who built the city but they do not get the credits and most of the time they are considered untouchables.
"Karuthavanalaam Galeejaam" means "Darskinned people are often misunderstood/promoted as not so good people"
"Velaikkaran" movie name means "Working-class people like labors, koolis, drivers, construction workers, etc..."