Open Set: In topology, an open set is a collection of points where every point has a neighborhood contained entirely within the set. It's like having an open box where all the points inside are accessible without crossing any boundaries.
Closed Set: A closed set is the complement of an open set. It contains all its limit points and doesn't have any gaps or holes. Imagine closing up a box with no openings - everything inside stays contained.
Homeomorphism: A homeomorphism is a continuous function between two topological spaces that has an inverse function also continuous. It essentially means that two spaces can be transformed into each other while preserving their topological properties. Think of it as being able to morph one shape into another without tearing or gluing anything - just smooth transformations.