terminal in my view is that station where the train gets originate & terminate is known as terminal,such as cst,rajendra nagar, anand vihar etc.
junction is that station where trains of two different direction meet at one point,such as itarsi junction where trains from nagpur side & mumbai side meet at itarsi & even depart for different side stations such as one side towards bhopal&other side towards jabalpur.junction can be called to any station which completes any one of the above .either two different side arrive at one station or depart for two different side from same station.