Quantitative data is data that is heavily grounded in numbers - how many users, what percentage of them are happy, what is the ratio of converted vs. non-converted users? All of these should be a topic for an entirely different post, however you see how you should not make product decisions exclusively based on qualitative data unless no other data is available and you are seeking product-market fit. To conclude - you use qualitative data to validate initial assumptions, and quantitative data to validate the direction and get hard numbers on whether your assumptions were correct.