Rendering is the process of turning a 3D scene into a 2D image. Blender includes three render engines with different strengths:
Eevee is a physically based realtime renderer.
Cycles is a physically based path tracer.
Workbench is designed for layout, modeling and previews.
More renderers from third-party developers are available as add-ons. Each renderer has its own render settings to control render quality and performance.
What the render looks like is defined by cameras, lights and materials. These are shared between Eevee and Cycles, however some features are only supported in one or the other.
Renders can be split up into layers and passes, which can then be composited together for creative control, or to combine with real footage. Freestyle can be used to add non-photorealistic line rendering.
Blender supports interactive 3D viewport rendering for all render engines, for quick iteration on lighting and shading. Once this is done, the final quality image or animation can be rendered and output.