Oregrounds iron was a grade of iron that was regarded as the best grade available in 18th century England.  The term was derived from the small Swedish city of Öregrund, the port from which the bar iron was shipped.  It was produced using the Walloon process.
Oregrounds iron is the equivalent of the Swedish vallonjärn, which literally translates as Walloon iron.  The Swedish name derives from the iron being produced by the Walloon version of the finery forge process, the Walloon process as opposed to the German method, which was more common in Sweden.  Actually, the term is more specialised, as all the Swedish Walloon forges made iron from ore ultimately derived from the Dannemora mine.  It was made in about 20 forges mainly in Uppland.
Many of the ironworks were founded by Louis de Geer and other Dutch entrepreneurs who set up ironworks in Sweden in the 1610s and 1620s, with blast furnaces and finery forges.  Most of the early forgemen were also from Wallonia.