UX research is the systematic study of users – their needs, behaviours and problems – through interviews, tests, surveys and data analysis, so that product decisions rest on evidence rather than guesses.
Research splits into qualitative (why? – in-depth interviews, usability tests, observation) and quantitative (how many? – surveys, analytics, A/B tests). The best decisions come from combining both: analytics shows where users drop off, interviews show why.
A common myth: "research is expensive and slow". In practice, five usability tests uncover most of a product's critical problems, and a week of research can save months of building the wrong feature.
When to research: before design (needs), during (prototype tests) and after release (behaviour analysis). Research is a continuous process, not a one-off ritual.