I think you are talking in terms of hybridization. Lets look at organic chemistry and the bonds between two carbons. A single bond is referred to as sigma bond. If we look at the number of valance electrons in carbon there would be four 2 in the 2S and 2 in the 2P level, yet carbon forms four identical bonds. This does not really make sense, why should a bond where both the electrons coming from the Carbon look identical to a bond where one is electron is coming from one carbon and one from another carbon.
Chemists use the hybridization theory to explain this in simple terms, one of the electrons in the 2S is somehow promoted to the 2P level (now each orbital holds one electron). The one S and three P's are then mixed together hence becomes SP3.
Now a double is a sigma bond and a pie bond. The pie bond is in fact the overlap of a p with another p orbital. This just leaves one S and two P's left to mix together and hence the sigma bond and any other single bonds next to a double bond is said to SP2 hybridized. If a C is bonded to a H it will be SP2-S bonded.
Triple bonds is a sigma bond and 2 pie bonds. Remember pie is the overlap of 2 P orbitals. Therefore all that is left for the hybridization is one S and one P hence SP1.