Simple Definition:

Sovereign means having supreme [complete] power or authority [control or ability to make decisions] over a territory or nation. It refers to a ruler or governing body that has the highest level of control and autonomy [independence or self-governance] within its borders. For example, a king or queen who has the final say in making laws and governing their country is considered sovereign. A person in a lower position who is bound by the decisions of the higher-ups, on the other hand, is not considered sovereign.

Very Simple Definition:

Sovereign means having the highest power and control in a country. For example, a king or queen who makes the laws and rules the land is sovereign.