Conceptual metaphor involves the comparison of two concepts in that one is construed in terms of the other. It's often described in terms of a TARGET DOMAIN and a SOURCE DOMAIN. The target domain is the experience being described by the metaphor and the source domain is the means that we use in order to describe the experience. For example:

We're wasting our time here.

This sentence is based on a metaphor “TIME IS MONEY” in which the target domain, TIME, is conceptualized in terms of the source domain of MONEY. Very often, abstract experiences are described in terms of more concrete ones. In cognitive linguistics, metaphors are represented by a simple formula: “X is Y”, in which X is the target domain and Y is the source domain.