Time

Time is the system through which we can determine and refer to when something occurred.

In terms of recorded music, the most relevant periods of time are the recent 20th century and the current 21st century, which can be divided into decades thusly:

the 1900s ?
the 1910s ?
the 1920s ?
the 1930s ?
the 1940s ?
the 1950s ?
the 1960s
the 1970s ?
the 1980s ?
the 1990s ?
the 2000s ?
the 2010s ?
the 2020s

And though they have not yet come to transpire, we can presume that eventually we will reach the 2030s ?, if we're lucky.