Instrumentals have existed since the beginning of music and it generally means it's a song without vocals. One of the leading releases in Instrumental HipHop was an artist named DJ Shadow whose album DJ Endtroducing..... Shot to popularity worldwide and even today is a highly sought after release. Other titans in the Instrumental scene are J-Dilla,MF Doom, Madlib & Nujabes who have all released huge projects that are widely acclaimed.
If you want to listen to music without vocals then Instrumentals are for you!