Black grape varieties, that are of course identical, it's simply that it is known by the former name in Europe and the USA, and by the later in South Africa and Australia. However, saying that, winemakers can, and do use either name, with examples labelled as Syrah usually emulating a classic northern Rhône, elegant and restrained style, and those labelled as Shiraz exhibiting a more fruit driven, riper, less tannic expression.
Some of the oldest Shiraz vines in the world are found in Oz, where it's grown more than any other red wine grape, and Barossa Shiraz is famous the world over. This dark skinned variety is high in tannins, loves stony granite soils, and is grown worldwide, producing powerful, full-bodied, intense wines as either a straight varietal or in a blend.
Its spiritual home is France's Rhône Valley, where it's used in the northern Rhône exclusively for the famous wines of Hermitage. It's also the major player in Côte-Rôtie, but this wine may also contain some Viognier.
In the southern Rhône it's used as a blending grape, most famously as one of the 13 varieties allowed to contribute to Châteauneuf-du-Pape. Where the wines have flavours of black fruits abound - blackberries, black cherries, damsons and plums, with wild herbs, chocolate, smoke and spice, particularly liquorice and black pepper. It can also develop the gamey characteristic as it ages.