Here is a pretty simple explanation:
“Most songs are written in the 4/4 time-signature. This means that one measure has 4 beats, and the quarter note represents one beat. In english, this means that you can count along to these songs as “one-two-three-four, one-two-three-four” etc. Take John Lennon’s Imagine. You can calmly count along to this the way I just mentioned. Dave Brubeck and his quartet played jazz, but he felt that the music was too tame, that there was more to jazz than the usual 4/4 time and the occasional 3/4, or waltz, time. With Time Out, he managed to break away from the usual time signatures. The first track throws you into the deep immediately with a stunning 9/8 rhythm, grouped as 2–2-2–3, a rhythm that Brubeck picked up in Istanbul, as he heard street musicians play music in this rhythm. Then there was a track in 6/4 time, another track which time-signature constantly vacillates between 3/4 and 4/4, and then..! Then, there was a track in 5/4 time. So, there were 5 beats in one measure, and the quarter note represented one beat. The drums and piano make the song swing lightly, the syncopations made the 5/4 time sound strangely familiar, the saxophone sounded beautiful, the bass and the piano made sure you wouldn’t lose count, the bridge of the song was great. In other words, it was a damn fine song.”