All of the atoms of a saturated hydrocarbon are bonded by 4 pairs of electrons in case of a carbon and 1 pair in case of hydrogen.
Saturated hydrocarbons are hydrocarbons with only single bonds. Each carbon has a maximum number of hydrogen atoms bonded to it. A good example is alkanes. On the other hand the unsaturated hyrocarbon are hydrocarbons with at least one double bond or triple bond.