what is the difference between graphs and spanning tree?

First of all, a graph is a "diagram that exhibits a relationship, often functional, between two sets of numbers as a set of points having coordinates determined by the relationship. Also called plot". Or A pictorial device, such as a pie chart or bar graph, used to illustrate quantitative relationships. Also called chart. And a tree is a connected graph that does not contain any nontrivial circuit. (i.e., it is circuit-free) Basically, a graph is a nonempty set of points called vertices and a set of line segments joining pairs of vertices called edges. Formally, a graph G consists of two finite sets: (i) A set V=V(G) of vertices (or points or nodes) (ii) A set E=E(G) of edges; where each edge corresponds to a pair of vertices. Whereas, a spanning tree for a graph G is a subgraph of G that contains every vertex of G and is a tree. It is not neccesary for a graph to always be a spanning tree. Graph becomes a spanning tree if it satisfies all the properties of a spanning tree.