User Research is the catch-all term for a wide range of qualitative and quantitative methods used to understand the issues people face when interacting with a product or a service - for example:

• User Surveys to map your existing audience and/or Persona Modeling to define the archetype users we are designing for.
• Ethnographic Observation, User Interviews and Log Analysis to understand the What, When, Where, Why and How of using your product, or your competitor’s product.
• Usability Testing throughout the product development cycle to identify pain points in an existing design, to help iterate solutions and to refine and validate the final product.

On bigger design projects I will typically insist on employing at least some of the above to inform the design, but if you already have design covered, feel free to order User Research à la carte.