Type A
Direct Answer
Type A is the ungrounded 2-flat-pin plug standard in North America, Central America, and Japan -- NEMA 1-15, rated 15A/125V. It's a physical subset of Type B: any Type A plug fits directly into a Type B socket, the ground pin recess simply unused.
Source: NEMA 1-15
Specs
| Pins | 2 flat parallel blades, non-coplanar, 12.7mm apart |
| Rated Current | 15 A |
| Rated Voltage | 125 V |
| Grounded | No |
| Common Regions | USA, Canada, Mexico, Central America, Japan |
A Subset, Not a Separate Standard
Type A (NEMA 1-15) has been prohibited in new US and Canadian residential construction since 1962, when grounded outlets became mandatory -- but it remains common on older buildings' outlets and on countless small two-prong appliances and chargers that don't need a ground connection. Japan uses the identical physical connector, just at a lower 100V supply voltage rather than North America's 120V.
Type A is not a competing standard to Type B so much as its predecessor and physical subset: a Type A plug's two flat blades are dimensionally identical to Type B's, so it inserts directly into a Type B socket with the ground-pin hole simply left unused. The reverse doesn't work -- a Type B plug's extra ground pin won't fit an ungrounded Type A socket.