Difference in use of rounded rectangle and normal rectangle

In any diagram be a uml or any software engineering model dia开发者_StackOverflow中文版gram whats the difference in using a rounded rectangle and a rectangle.? ----Thanks in advance

For UML specifically, rectangles are generally used for structural concepts: classes, objects, packages. Rounded rectangles are used for behavioural concepts: states, activities.

There's no "universal" software engineering convention I'm aware of.