Admittedly, it is difficult to get lost on the M3. You just sit tight and follow the road. If, however, you suddenly find yourself within spitting distance of Trafalgar Square, or the QE2, you have probably missed a turn somewhere.
The shape of a tune
Just as most pop and rock tunes have a recognizable shape that allows you to identify the 'verse' and the 'chorus', most jazz standards have a very rigid structure that is 'looped' a number of times. The most common is the so-called AABA shape. The A's are usually almost identical sections, and the B section, sometimes called the bridge, is supposed to be a kind of contrast to the A's. The final A often contains a few twists to indicate that the end is coming up. The A section is not far off being equivalent to the verse in a pop song whereas the equivalent of a chorus doesn't really exist in jazz. Incidentally, jazz musicians refer to the whole tune (the structure which is being looped) as one chorus. A solo typically stretches over at least a couple of choruses but the exact number is usually never agreed on in advance. When the improvisor runs out of steam, looks are exchanged, and the band moves on.
The classic bossa Girl From Ipanima (mp3) is a typical AABA tune. I have added a four bar intro, and a four bar ending. The A sections are 8 bars long, the B section is 16 bars long.
The A sections in an AABA tune can be variations on the same theme. In All The Things You Are (mp3) the second A is a transposed version of the first A.
The most original tunes are, of course, the ones that evolve in a natural way without making you notice their structure at all. Herbie Hancock's beautiful tune Dolphin Dance (mp3, pdf, tef) consists of a 34 bar structure following a four bar intro, and it flows very smoothly from start to end.
Wayne Shorter's extraordinary ballad Infant Eyes (mp3) has an ABA shape with each section lasting 9 bars, making it a 27 bar structure.