"Lifeworld" (or Life-World, in German: Lebenswelt) is a concept Edmund Husserl borrowed from Wilhelm Dilthey to designate the world as it presents itself to a naive (non-scientific) perception. Husserl reproaches the modern sciences for having dug an impassable gap between themselves (the world of science) and the Lifeworld (see his critique of psychologism). As part of the call "back to things themselves", Husserl wants philosophy back in the world of life, not of speculative thought.
Therefore, Husserl used the concept of lifeworld to discuss the world surrounding the individual. which is perceived by him subjectively as the real world. The specificity of such a view of the world is the lack of doubts as to its reality. Life-world can be understood as the world of everyday life, everyday experiences and activities of an individual, but also the world of dreams, fantasies and religious experiences.
Husserl describes the lifeworld as "originary” and "unitary". From to pespective of Phenomenology, adressing the lifeworld gives acces to the origin of experience and the original unity of phenomenon and things.
See also:: What is Phenomenology?