An explanation is a statement which points to causes, context, and consequences of some object, process, state of affairs, etc., together with rules or laws that link these to the object. Some of these elements of the explanation may be implicit.
Explanations can only be given by those with understanding of the object which is explained.
In scientific research, explanation is one of three purposes of research (the other two being exploration and description). Explanation is the discovery and reporting of relationships among different aspects of studied phenomena.
Some different types of explanations:

Deductive-nomological
Functional
Historical
Psychological
Reductive
Teleological
Methodological