If you name one or more executors to carry out the terms of your Will (co-executors), the substitute co-executor is the person you name to replace a co-executor if they are unable to work with the other co-executor(s) to carry out the terms of your Will.
For example, let’s say you name Jacob Barringer and Malik Williams as co-executors and you name Asha Davis as the substitute co-executor. If Jacob cannot serve as co-executor with Malik, then Asha will step in and Malik and Asha will be co-executor.