boundary

noun
  1. A line or limit that marks the edge or extent of something, often used to define the physical or conceptual limits of an area or object. noun
    The river serves as the boundary between the two countries.
    The fence marks the boundary of the property.
  2. A limit of a subject or sphere of activity, often used in a metaphorical sense to describe the limits of behavior, thought, or interaction. noun
    It's important to set boundaries in a professional relationship.
    The discussion pushed the boundaries of traditional thinking.