qualitative analysis
Open a kitchen cupboard and ask only one thing: what is in here? Not how many cans, just which foods are present — flour, salt, sugar. That kind of 'what is here' question is qualitative analysis. It tells you which substances a sample contains, without (yet) worrying about how much of each there is.
Qualitative analysis is the identification of the chemical species present in a sample. The answer is a name or a yes/no, not a number: this water contains chloride; this powder is aspirin; this stain is blood. Chemists reach such answers through characteristic reactions, colors, melting points, or instrument fingerprints unique to each substance.
It matters as the natural first step: before you can sensibly ask 'how much', you usually need to know 'of what'. The caveat is that a clean qualitative answer can be surprisingly hard — two substances may give similar tests, and very small amounts may slip below what a test can detect, so 'not found' is not the same as 'not present'.
Adding silver nitrate to a solution and seeing a white precipitate form is a classic qualitative test: it tells you chloride is present, but on its own it does not tell you how much chloride there is.
Qualitative analysis answers 'what is present', not 'how much'.
A negative qualitative result means 'below the detection limit of this test', not 'absolutely zero'. Always read it together with how sensitive the test is.