I am working with biofilm and there are many documents talking about boudary conditions while others talks about interface or both of boundary and interface. So, boundary and interface are the same (in numerical analysis) or not? why and examples?
I'm not particularly familiar with biofilm literature. But in most computational literature, the border of the entire domain of a problem are usually referred to as the boundary. Outside of a boundary, there are no nodes, elements, or anything else under consideration.
The entire domain may also be subdivided into smaller regions. Some of these regions share edges on the boundary of the domain. However, some of these regions share borders between each other that are not boundaries of the domain. Usually these regions have different material properties or different relevant physics and may also have different meshes. The borders between any two regions in a domain are usually referred to as interfaces.