A listed jump is any jump listed in the rules with a set point value. For instance, an axel is worth 0.8 points, a triple axel is worth 7.5 points, etc.

A non-listed jump is any of a number of jumps not listed, like a reverse axel. It's considered a transition or footwork element - Johnny did one in his straight-line footwork at Worlds in 2004 - but it doesn't score any points or count as a jumping pass. Other non-listed jumps are half-loops and waltz jumps, or, potentially, a weird new jump that a skater invents.

Occasionally, a skater will pop an axel jump into a waltz jump. If they think fast, they'll realize they could try the double or triple axel again, since the waltz jump didn't use up a jumping pass. (A waltz jump takes off forward, like an axel, but only turns a half-revolution before landing).

If a skater connects two double or triple jumps with, say, a half-loop, it counts as a jump sequence, one of the three allowed. But if a skater has a wonky landing on a triple and does an inadvertent half-loop, which happens pretty often, the rules are explaining that they can still do their three jump combinations/sequences in the program.

A half-loop, by the way, takes off on a back outside edge and lands on the inside edge of the opposite foot. For Johnny, he takes off the left back outside edge and lands on the right back inside edge. People do half-loops in the middle of jump sequences, since it sets up the takeoff for a salchow jump, or, I suppose, a flip.

It's hard to explain if you don't skate!