There are two types of delays, those with Cancel selected and those without. As @dan.t says, Cancel Delayed Actions cancels those that have Cancel selected. Delays without Cancel can also be cancelled with the Stop Actions This Rule action (or by another rule). Think of the Cancel toggle as making that delay eligible to be cancelled by Cancel Delayed Actions.
There is a parallel mechanism for Repeats, those with Stop selected and those without. Stop Repeat Actions will stop any repeat with Stop selected, but not a repeat without it selected. And, Stop Actions will stop all repeats (can be done by another rule).
