These music lyric charts are made by Nickolay Lamm and are part of his project called 'Money, Love and Sex.' The project graphs the frequency with which various words appear in the top 100 singles on the Billboard chart. The graph exemplifies the most popular words used over the years.
The graphs essentially create pictures of how the vocabulary of music is evolving since the 60s. The horizontal axis is the year of the song and the y-axis is the song's popularity dependent on the Billboard Year-End Hot 100 singles. Each single cell represents a song. The more red a song appears on the chart, the more often that specific word appeared in the song.
It is no surprise that the music lyrics charts have the word 'love' being very consistent, or that curse words have increased on the years with rap music becoming more and more prominent on the radio and television.