What is the concept of a universe? how is it different from a "multiverse"?

The universe is all of time and space and its contents that we live in, described by a set of physical laws and constants. however, a multiverse is a hypothetical set of finite or infinite universes, each with its own set of different space-time configuration and  physical laws and constants. 

answer and explanation;

composition refers to both the types of minerals within a rock and the overall chemical makeup of the rock while texture refers to the size and arrangement of the minerals or grains that make up a rock. both composition and texture can be used to classify rocks, such as igneous rocks. texture describes how the rock became solid or crystallized from liquid, melted rock. composition of a rock describes the minerals that make up a particular rock.