What Catch on Bound baseball?

Catching the ball "on (a) bound" means that it was caught on one bounce. In the early days of baseball (the 1850s), if you caught the ball on the first bounce, it was an out. The rule books of the time called this a "catch on bound".

In 1865, the rules were changed so that fair balls needed to be caught on the fly to be considered an out, but foul balls could still be caught on one bound for an out.

In 1883, the National League changed the rule so ALL balls needed to be caught on the fly for an out. The American Association (another league) still allowed foul balls to be caught on one bound for an out.

In 1891, the two leagues merged, and the National League rules were followed, eliminating all "caught on bound" outs.

Source: http://www.19cbaseball.com/rules.html