sp hybrid orbitals are a combination of one s and one p atomic orbital. This leads to two sp hybrid orbitals that are arranged in a linear geometry.
Thus, any center with a linear electronic geometry is sp hybridized.
As only one p orbital is "used," there are two "left-over" p orbitals on the atomic center. Each of these could overlap with an appropriately oriented p orbital on a neighboring molecule and form a pi bond. As there are two p orbitals, these could be double bonds or there could be a triple bond.