A process that whenever it’s instantiated can logically be relied upon to produce a predictable result.
There are three key features to it:
1) Substrate Neutrality: The results are due to the logic of the process, not the powers causing the process. Prescribed steps must be followed exactly for a process to be considered to be algorithmic.
2) Underlying Mindlessness: An idiot or computer has to be capable of performing the tasks. The recipes have to be very simply written in manner that is exceedingly easy to understand and follow.
3) Guaranteed Results: The process should yield anticipated results if operated without missteps.
“An algorithm is a certain sort of formal process that can be counted on — logically — to yield a certain sort of result whenever it is ‘run’ or instantiated” (50, Darwin’s Dangerous Idea)
Darwin’s Dangerous Idea by Daniel Dennett