[failrate]

The best example I can think of is a set of instructions on a medium. You've got jumps as a normal part of programming at this level. If the address of the jump is corrupted by an environmental factor (e.g. Hard radiation), then the jump may end up in lalaland. A sled in this context would be placed at the end of and in between sets of instructions with a jump back to a safe location to restart. So a jump to an invalid location or past the instruction set would have a chance of recovering back to a valid subroutine.