DoubleEntryAccounting
Directly quoting bkuhn from #npoacct @ irc.freenode.net:
│17:31:34 bkuhn | oh, reason is easy: in the USA, any bookkeeping system that isn't double-entry would │
│ | likely not be considered appropriate GAAP │
│17:31:50 bkuhn | you can link GAAP to │
│ | http://en.wikipedia.org/wiki/Generally_accepted_accounting_principles │
│17:31:54 bkuhn | GAAP is an odd thing. │
│17:31:58 bkuhn | It's not the "law" │
│17:32:10 bkuhn | but accountants would tell the IRS "we think something bad is going on" if you didn't │
│ | follow GAAP │
│17:32:20 bkuhn | Also, GAAP isn't a list of rules. │
│17:32:29 bkuhn | It's basically 'rough consensus' of accountants │
│17:33:08 bkuhn | So, it's somewhere in between "implicit norm" and the "law" │
│17:33:27 bkuhn | in the sense that you'd probably loose your non-profit status from the IRS if your │
│ | auditors said you weren't following GAAP
For convenience: Generally accepted accounting principles [wikipedia]