This plug is used in much of continental Europe.  The name "Schuko" is derived from the German word 'Schutzkontakt', meaning grounded plug.
The engagement surface is recessed due to the unusual grounding. As a bonus this makes it impossible to touch live pins.

Grounded plugs fits both grounded and ungrounded socket outlets, but the old round ungrounded plugs do not fit grounded socket outlets.
Socket outlets of this type also accept the flat ungrounded Euro-plug and shaped ungrounded plugs.

In Italy special versions of the Schuko socket outlet can be found that also accept the Italian 10A and sometimes 16A plugs.

Very often Schuko plugs, like the one on the picture, also feature a hole for the ground pin of French socket outlets.
(A frenchman would of course say that these are French plugs that also feature German grounding)

The Schucko also fits Danish socket outlets, but the ground does not make contact.

Pins are on 19 mm centers, 19 mm long and 4.8 mm in diameter.
Maximum current 16A, but very often outlets are fused at 10A or less.
Standard: CEE 7/7 (French/German combination plug)