As the name suggests, quantitative refers to a group of methods whose main focus is on quantities, that is, numbers. Numbers will usually be the main type of data that these methods collect, and those numbers will be analysed using mathematical or statistical techniques. Researchers using quantitative techniques usually see themselves as doing science.
Experiments done in a laboratory will almost certainly be quantitative. In a health care context, randomised controlled trials are quantitative in nature, as are case-control and cohort studies. Surveys (questionnaires) are usually quantitative .