A cancellation is when a player is considered inactive. For example, if an NBA player plays less than 0 minutes, then they will be considered inactive. This means that the question will be canceled and that your entry will regress 1 pick, so if you have a 4-pick entry, then it becomes a 3-pick entry. For further information on cancellations, please see the article here.
A Rescue Refund is when an active player leaves injured in the 1st half of a game (amongst other qualifiers) and is the sole reason your entry lost. You will then receive the relevant promotional funds. For more information on what picks and entries qualify, please see the article here.