A campo (field) is a square. The only piazza is Piazza San Marco.
A campiello or a campazzo is a small square.
Rio is a canal.
Rio terà is a canal that has been filled in. You can easily detect this by the different disposition of the pavement slabs.
Piscina is a pool or turning basin that has been filled in to become a square.
Calle is the name of a street.
Ruga is an important street, usually lined with shops.
Fondamenta and Riva define a wide street running along a canal.
Ramo (branch) is a short street or an extension of another street with the same name.
A salizzada indicates a paved street (once rare).
A sottoportego is an arcade or arched passage under a building.