Ideally you want to be in fifth gear on the motorway but given the unpredictable amount of traffic on the M3, particularly as you get close to the M25, you find yourself using all of them at some point. Apart from the reverse, hopefully.
Rythm and Meter
Swing feel and straight eights
The swing feel, which to many people is the defining element of jazz, is contrasted by the straight eights feel, which is used mainly for latin tunes and other types of groove-oriented material.
There are actually some tunes that alternate between straight eights and swing feel. Green Dolphin Street (mp3) starts off in straight eights, latin style, and then goes to swing. The rather corny midi backing band on my recording makes it easy to hear when the transition occurs.
The straight eight groove classic of the jazz-genre is Cantaloupe Island (mp3, pdf, tef) by Herbie Hancock. I have taken the opportunity to let my Carvin do a Strat impersonation.
The Chicken (mp3) by the legendary Jaco Pastorious is another great funky tune. It sounds best with an electric bass so it is called on jazz gigs only rarely. Double bass players struggle with this one, understandably.
The meter essentially defines the subdivision of the rythm. If a tune is in 3/4, you will be in sync with the rythm if you count "one two three one two three...". If it is in 4/4, you will be in sync if you count "one two three four one two three four...". The examples in the section above (Green Dolphin Street, Cantaloupe Island, and The Chicken) are all in 4/4.
Contemplation (mp3) is a simple tune in 3/4 swing feel, also referred to as a jazz waltz (if you have ever done ballroom dancing you know that the basic sequence of steps in the waltz divide into groups of three). The first time through the recording includes the chords only, during the second chorus the melody is added.
Almost all jazz-standards are written in meters whose numerator divide by 3 or 4. The one exception that you should be aware of is Take Five (mp3), which is in 5/4. A lot of pop- and funk tunes are in 5 (Sting's Seven Days, for example) and 7 (Money by Pink Floyd, for example) but for some reason jazz is quite conservative in this respect.