A "suspension" is a musical device in which a change in harmony happens but one note is left behind, usually one too high (occasionally one too low) and it falls into line on the next beat. While it hangs suspended, the note stands out as dissonant, and then when it falls in line there is a satisfying feeling that harmony has been restored. Suspensions became a favorite during the 16th century, and they've never gone out of style since. By the early 19th century, Chopin could write into this etude one suspension leading to another to another, so that we listen with a sense that just as one note is resolved, there's another that's hanging.
An etude is a study piece, presumably meant more for a student's learning experience than for an audience's listening pleasure. Chopin wrote 27 etudes, (Op 10, Op 25, and three more after he was dead, which is a good trick by any stretch) and -- just to make a point, I think -- he included some of his most beautiful melodies in the etudes. I think he was sending a message, "just in case you think this is a boring student piece""
I fell in love with one of the posthumous etudes last week, and spent a few hours learning to play it. The melody is simple, based on notes repeated 2, 3 or 4 times each. The interesting thing is that as the melody notes repeat, the notes underneath are subtly shifting. We say the "inner voices" are moving even as the melody and bass, which you hear most prominently, stay constant.
I had trouble finding a recording in which you can really hear the inner voices moving, so I tried to make one myself, by playing more slowly, slowing imperceptibly before some of the inner voice changes, and playing the inner voices a little louder than they might otherwise be played. I count the experiment a failure--I like Edna Stern's recording far better than my own, even after I allow myself a few gaffs and goofs. Stern, by the way, is playing on a Pianoforte styled after one from the early 19th Century, such as Chopin might have played. The tones don't resonate as long and the overtones are less rich than a modern piano, so it sounds just a bit plinky.