The number of hydrogen atoms associated with a given skeleton of carbon atoms may vary. When the chain or ring carries the full complement of hydrogen atoms, the hydrocarbon is said to be "saturated". Such hydrocarbons are known as paraffins, paraffinic hydrocarbons, or alkanes/cycloalkanes. The "paraffin" term was common in the oil industry, because of the waxy characteristics of crude which contains these molecules. The term "alkanes" is common among chemists.
Straight-chain structures are "normal paraffins", branch-chain structures are "isoparaffins", and ring-type structures are "cycloparaffins" or naphthenes. Thus for three hydrocarbons with five carbon atoms (i.e. all "pentanes") we have several structures.
The branch-chain creates Isopentane, illustrated below:
An example of the ring-type structure, the slightly more complex cyclohexane is shown below:
To learn about unsaturated hydrocarbons, click here.