Quantitative data is expressed in numbers. It comprises measurements of variables which, by statistical analysis, can be organised - totalled, averaged, etc. - into meaningful information. The results of the analysis can be used to draw conclusions about the event being studied.
The researcher is looking for relationships among the data - ways in which one set of data can be compared and evaluated with another. This is the purpose of statistical analysis. The results obtained can assume the status of "facts" since they are supported by scientific method. This would be the positivist perspective. Alternatively, there is a valid argument that the choice of analysis can influence the results, and looked at another way, the same figures might yield different conclusions.
Note that quantitative data is not limited to measurements of events or incidences that naturally occur in numbers - transactions, frequencies, etc. It is also possible to measure attitudes, by the use of ratings scales - a feature of surveys.