There are two main types of data that you might encounter.  The first is discrete data, which is a count of whole events, objects or persons.  For example, the number of people with a certain illness is a discrete quantity.

The other type of data is continuous data, which is the measure of a quantity such as length, volume, or time, which can occur at any value.  For example, the concentration of glucose in the blood is a continuous quantity.  Even if the instrument you are using rounds off values to whole numbers, these quantities are still continuous.