Zante Grapes are very small grapes. Usually only a maximum of 1/4 inch (1/2 cm) wide, they are about the size of a pea -- or "pearl", as the marketers today are saying (accompanied by the phrase "jewel-like" as well.) Their purple skin is so dark it is sometimes seems almost black. They grow in long clusters, and are seedless. The grapes are very sweet and tender, and have very small stems that are edible.
Wild versions of the grape have fruit no bigger than the tip of a pen, with very few berries per cluster. Cultivated Zante vines are either "girdled" (a strip of bark is taken off a small portion round the vine) or given a plant hormone called "gibberellic acid." This causes the vine to produce not only bigger grapes, but to grow bigger, fuller clusters as well. This required process, though, makes them not really suitable for home gardening.
The market for these grapes had always been for drying them into "currants", though technically they are raisins. American growers, however, are now trying to build a market by selling them as fresh grapes to eat out of hand. One of the monikers under which they are being sold is "Champagne Grapes", reputedly because they are so small that they appeared to someone to look like Champagne Bubbles. While the grapes are not actually used for making Champagne at all, no doubt if people think they are also used to make a high-quality wine, marketers won't object.
Zante is the name of one of the Greek Ionian islands (actually called "Zakynthos" in Greek) which is south of Corfu near the entrance to the Gulf of Corinth. The Zante Grape was planted there in 1516, in order to supply growing demand in Europe. The name of the island was shortened to Zante by the Venetians, who held the island as part of their mini trading empire in the 1600 and 1700s. The tax on the currants produced from the grapes boosted Venetian coffers. The Venetians were forced to hand the island over to Napoleon in 1797, during which time production slumped. The currant trade boomed again during the British protectorate period (1815-1864), but went into decline when the British ceded the island to a uniting Greece.