[al_f]

Not sure how familiar you are with GTD, so....

In Getting Things Done, any task you want to accomplish is either a project (if it requires more than 1 physical action step, e.g. "replace lightbulb in hall" which requires you to check the bulb needed, buy the bulb at the shops then replace it) or a single action step if it only involves 1 physical action/can't be sensibly broken down into smaller component parts (e.g. "water plants in kitchen").

Singletons are OF's way of dealing with these single action steps by grouping them into a project that is really just a group of these actions, a bucket to put them in if you will. Debate has raged on here (and is still) about whether this is the best way to implement this or not.