This kind of plug is called Schuko and it's a de facto standard in many European countries.
From Schuko - Wikipedia:
"Schuko" ( /ˈʃuːkoʊ/) is the colloquial name for a system of AC power plugs and sockets that is defined as "CEE 7/4". A Schuko plug features two round pins of 4.8 mm diameter (19 mm long, centers 19 mm apart) for the live and neutral contacts, plus two flat contact areas on the top and bottom side of the plug for protective earth (ground). Schuko sockets form a cavity into which the plug is inserted. Schuko plugs and sockets are symmetric AC connectors. They can be mated in two ways, therefore live and neutral can arrive on either pin at the consuming device. As with most types of European sockets, Schuko sockets can accept europlugs. Schuko plugs are considered a very safe design when used with Schuko sockets but they can also mate with other sockets to give an unsafe result.
"Schuko" is a short form of the German term Schutzkontakt (literally: protective contact), which simply indicates that plug and socket are equipped with protective-earth contacts (in the form of clips rather than pins). Schuko connectors are normally used on circuits with 230 V, 50 Hz, for currents up to 16 A.