Some of the features of the different organisms in a species show continuous variation, and some features show discontinuous variation.
Human height is an example of continuous variation. It ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these values. So it is continuous variation.
For any species a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are:
If you record the heights of a group of people and draw a graph of your results, it usually looks something like this:
The more people you measure, and the smaller the categories you use, the closer the results will be to the curved line. This shape of graph is typical of a feature with continuous variation. Weight would give a graph similar in shape to this.
A characteristic of any species with only a limited number of possible values shows discontinuous variation. Human blood group is an example of discontinuous variation. In the ABO blood group system, only four blood groups are possible (A, B, AB or O). There are no values in between, so this is discontinuous variation.
Here are some examples: