OffMesh Links are used to create paths crossing outside the walkable navigation meshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary surface. For example, jumping over a ditch or a fence, or opening a door before walking through it, can be all described as OffMesh links.
We’re going to add an OffMesh Link component to describe a jump from the upper platform to the ground.
Now you have a functioning OffMesh Link set up! If the path via the off-mesh link is shorter than via walking along the Navmesh, the offmesh link will be used.
You can use any game object in the sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary to hold the OffMesh link component, for example a fence prefabAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More info
See in Glossary could contain the OffMesh link component. Similarly you can use any game object with a Transform as the start and end marker.
The NavMesh bake process can detect and create common jump-across and drop-down links automatically. Take a look at the Building OffMesh Links Automatically for more details.