Quantitative is data you can count (analytics, surveys); Qualitative describes characteristics (customer stories, feedback).
Quantitative data tells you what is happening (e.g., "users are dropping off at the pricing page"). Qualitative data tells you why it’s happening (e.g., "the price feels unfair because they don't understand the value"). If you only look at one, you are flying half-blind. You need both to build a product people actually want to keep.