An expression of desire (I fancy that) or surprise (fancy that, it works).
Hopefully the first works for you but it was writ with the second in mind.
It is an experiment in musical form.
Music usually starts life as a riff: a short musical idea a couple of seconds long. Extending a riff to 8-16 bars forms a section, the building block of music. Repeating and varying sections and welding them together eventually results in a complete piece of music. The issue is how best to weld them together.
A shortish piece of music, such as a pop song, usually has no more than three sections. Fancy That has six. It is a good way to use up old riffs stored away in the attic that have never seen the light of day.
The easiest approach is to string the sections together in a sequence and call the thing a medley. Fancy That does exactly that and plays all six sections in sequence, ABCDEF. It is simple to do and can sound quite effective if the sections mesh with each other. The downside is that there is no common thread running throughout the music.
One approach that does use a recurring motif is a rondo. It has a short main theme, section A, interleaved by longer sections. Fancy That was converted into a rondo, ABACADAEAFA, but did not sound quite right (to my ears).
Another option is arch form. This is essentially a medley that cycles forwards then backwards through the sections. It is also called palindromic form, because it is the same forwards as backwards. Fancy That in arch form, ABCDEFEDCBA, sounded better than the medley and the rondo but was still not quite there.
Welding sections requires experimentation. Some will mesh together well, others will not, no matter how much they are tweaked. Tempo is another factor. Section E, the longest section, was written for a slow reggae song, which meant adjusting the speed of the other sections. Key is an issue too. All the riffs were initially written, as shown, in the key of C, but in the final version, section A is in E, section C and the first section D are in A, and the rest are in D.
Fancy That eventually wound up as ABCDEFDCA, a structure that is duly christened: the fallen arch.
Title: Fancy That
Length: 3' 17"
Track 1: harmonica melody
Track 2: viola harmony
Track 3: grand piano
Track 4: nylon guitar
Track 5: fretless bass
Track 6: drumset
Genre: Pop, Rock