The Danish straits are the straits connecting the Baltic Sea to the North Sea through the Kattegat and Skagerrak. Historically, the Danish straits were internal waterways of Denmark; however, following territorial losses, Øresund and Fehmarn Belt are now shared with Sweden and Germany, while the Great Belt and the Little Belt have remained Danish territorial waters. The Copenhagen Convention of 1857 made all the Danish straits open to commercial shipping.^[1] The straits have generally been regarded as an international waterway.

Toponymy and geography

Five straits are named 'belt' (Danish: bælt), the only ones in the world^{[clarification needed]}. Several other straits are named 'sound' (Danish, Swedish and German: sund). Where an island is situated between a "belt" and a "sound", typically the broader strait is called "belt" and the narrower one is the "sound":

• Als:
  • separated from the continent by Alssund
  • separated from Fyn by the southern part of the Little Belt, an area referred to in German (but not Danish) as Alsenbelt
• Fehmarn
  • separated from the continent by Fehmarnsund, also Femersund
  • separated from Lolland by Fehmarnbelt (German) / Femerbelt (Platt) / Femernbælt (former spelling: Femer Bælt)

• Langeland:
  • separated from Tåsinge Island by Siø Sund (Tåsinge itself is separated from Fyn by Svendborg Sund)
  • separated from Lolland by Langelandsbælt, the southern part of Great Belt
• Lolland:
  • separated from Falster Island by Guldborgsund (Falster itself is separated from Zealand by Storstrømmen Strait)
  • separated from Langeland by Langelandsbælt
  • separated from Fehmarn by Femernbælt, which is the common continuation of Great Belt–Langelandsbælt and Little Belt
• Zealand (Danish: Sjælland)
  • separated from Scandinavian peninsula of the continent by Øresund (Danish) / Öresund (Swedish)
  • separated from Fyn Island by the Great Belt

Etymology of "sound" / "sund"

The Germanic word "sound" has the same root as the verb to sunder in the meaning of "to separate". The Old Norse form of that verb is sundr. In Norway hundreds of narrow straits separating islands and combining fjords or outer parts of fjords are named "Sund".

Another explanation derives "sound" from an ancient verb "sund" in the meaning of to swim. That way a sound is a swimmable strait. In the Swedish language any strait is called "sund".

The Germanic word "sound" is not related to the Romance languages originated word "sound", which has developed from the Latin sonus.^{[citation needed]}