First, lets break down what "Viking" means.

There is some confusion between the terms "Viking" and "viking".

In the nomenclature of history and archaeology, Vikings are the Early medieval people of Scandinavia, and the colonies elsewhere. The name is not something the likely used for themselves, but a moniker used by modern historians to name their extended Culture.

As for the lower case v term "viking" this is a term that in Old Norse described an activity, which included piracy, but was probably more than that. the etymology of the word is complicated, and but can mean "Piracy "(I viking), sailing through small bays (vik-) and rows of roving men on a ship (vyk-). All those theories are plausible, but In my view, the correct translation should be "adventuring", as it would encompass piracy, raiding, exploration,, trade, war, all of which was done on such expeditions.

On the other end, "piracy" traditionally means attacking one ship with another, the crew boarding the attacked ship and either killing, enslaving or mugging the victims at sword-point.

Also, distinction must be made between "pirates" and "corsairs". The first are freelancers, the second are hired on purpose by a local lord to ravage their enemy's ships, and thus, are mercenaries of sort.

Now, while the Vikings sometimes did attack ships, their more common form of armed assault was raiding a coastal town or a village, and using the ships only for transport.

So, if you wish to be more accurate, Vikings were raiders rather than pirates. Ato of that, they were quite often mercenaries or recruited by a king or major jarl, thus making them corsair raiders rather than pirate raiders.

As for your second question, a group contemporary and almost identical to Norse vikings were Slavic Chąśnicy. These corsairs and raiders operated very similarly to vikinging Northmen, attacking ships and coastal settlements, though the main difference was that they more often backed by local Slavic princes and dukes, and not independent adventurers and warlords.

Chąśnicy and Norse vikings clashed often. They battled over the Wolin emporium. They clashed at Svold. Finally, they destroyed the Viking cities of Hedeby, Konungahela and Aarhus. In the end, the Slavic pirates and Viking pirates made truce when both groups were united under the Danish king Canute VI, after Chąśnicy were soundly defeated during the battle of Zingst, in 1184.

Source:

Jesch, Judith (2001). Ships and Men in the Late Viking Age: The Vocabulary of Runic Inscriptions and Skaldic Verse

Mechło W., Chąśnicy: słowiańscy wikingowie, Szczecin 2005.