In ethylene, the C=C double bond consists of a sigma bond and a pi bond. The sigma bond is formed by the head-on overlap of two sp2 orbitals. The pi bond is formed by the side-on overlap of two 2p orbitals.
A triple bond contains one sigma bond and 2 pi bonds.
In acetylene, the C≡C triple bond consists of a sigma bond and two pi bonds. The sigma bond is formed by the head-on overlap of two sp orbitals. The pi bonds are formed by the side-on overlap of 2p orbitals.