In general, it means a fresh sausage meant to be cooked, as opposed to salame, which are generally cured and ready to eat. Roman writers gave the credit for their invention to the ancient Lucanii, who lived in what is now the Basilicata, and lucanica or luganega is still a common name for them.
As you would expect, Italy has hundreds of different recipes all over the country. There are sausages of pork, beef, turkey, goose, buffalo or any mix of the above, liver sausages, offal sausages, sausages with greens or pine nuts inside, boar and deer sausages, sausages flavoured with honey or fennel (very popular) or coriander or peperoncini.
Sometimes it's hard to know where a salame starts and a salsiccia ends. Famous salsiccia di Calabria (Casanova really liked it) is really a salame.
Six kinds are in the Ark of Taste:
salsiccia di Bella-Muro (Basilicata): rare, high quality pork sausage.
salsiccia di Bra: a rare Italian beef sausage that owes it origins to the once important Jewish community in nearby Cherasco. Once originally all beef, today its ingredients include pork fat.
salsiccia di Cancellara (Basilicata): made of the less choice cuts of pork, mixed with lard spiced up with chillis.
salsiccia di Monte San Biagio DOP: This sausage from Lazio is flavoured with toasted coriander seeds, along with moscatelle and hot and sweet red pepper. In March, Monte San Biagio holds a popular Sagra di Salsiccia.
salsiccia sgranata: sausage meat
salsiccia rossa di Castelpoto: an artisanal sausage made near Benevento in Campania from fine pork cuts, and flavoured and coloured red with sweet and hot chilli peppers.
salsicciotto Frentano: made in Frentano in the Abruzzo and otherwise known as saiggicciott and sauccicciott, it's made of top cuts of meat and is considered the leanest of all Italian pork sausages.