Two bodies are said to be in contact when they share same boundary and the boundaries are constrained by a relation, for example no relative movement.
A geometrical domain can be divided in multiple subdomains. For solid mechanics simulations this could be the case for example for an assembly design consisting of multiple solid bodies (e.g. a clamp containing several rods and bolts etc). In this case the domain is discretized using a mesh operation by multiple non-conforming mesh parts, i.e. the single bodies are meshed separately by the meshing algorithm and do not share the nodes lying on their contact entities. In order to ensure the connection between those bodies, they have to be tied via contact constraints that couple the affected degrees of freedom.
There are three types of contacts available in the platform: