A star tree is a tree having a single internal vertex and n-1 leaves.

A tree is a connected acyclic graph, meaning that it consists of a set of vertices and edges, where each edge connects two vertices and there are no cycles (loops) in the graph. In a tree, there is a unique path between any pair of vertices.

A star tree is a specific type of tree that has a distinctive shape resembling a star. It consists of a single internal vertex, also known as the center or hub, and n-1 leaves, which are the endpoints of the edges connected to the internal vertex. The internal vertex is connected to each of the leaves, but the leaves are not connected to each other.

Example:
Let's consider an example to illustrate a star tree. Suppose we have a star tree with 5 leaves. The tree will have 6 vertices in total - one internal vertex and five leaves.

Internal Vertex:
- The internal vertex is the center of the star tree.
- It has a degree of n-1, where n is the number of leaves.
- In this example, the internal vertex will have a degree of 4.

Leaves:
- The leaves are the endpoints of the edges connected to the internal vertex.
- Each leaf has a degree of 1, as it is connected only to the internal vertex.
- In this example, each of the five leaves will have a degree of 1.

Edges:
- The edges connect the internal vertex to each of the leaves.
- In this example, there will be five edges connecting the internal vertex to each of the leaves.

Properties of a star tree:
- A star tree has n vertices, where n is the number of leaves.
- It has n-1 edges, connecting the internal vertex to each of the leaves.
- The internal vertex has a degree of n-1, while the leaves have a degree of 1.
- The leaves are not connected to each other, only to the internal vertex.

Conclusion:
In summary, a star tree is a specific type of tree that consists of a single internal vertex and n-1 leaves. The internal vertex is connected to each of the leaves, and the leaves are not connected to each other. This structure gives the tree its distinctive star-like shape.