Most statisticians prefer to classify data as being either qualitative or quantitative.

Qualitative data: The data describes something in words, not numbers. Often (not always), such data captures feelings, emotions, or subjective perceptions of something.

Quantitative data: The data describes something in numbers. Often (not always), such data includes measurements of something.

Examples:

Item                   Qualitative                                               Quantitative

Colour                       Blue                                                             460 nm

Height                       Tall                                                               1.72 m

Weight                    Heavy                                                          1000 Tonnes

Temperature           Hot                                                                110 F

As you can see, if the data is qualitative, the descriptions are in words. However, the same items are described in numbers when the data is quantitative.

For the purpose of statistical analysis qualitative data may be transformed (converted) into quantitative data by assigning numbers to the words.

http://en.wikipedia.org/wiki/Blue