Geometry Terminology
FEFLOW applies a finite-element technique, providing a discretized solution. For this, the modelling area is subdivided in nodes and elements as part of a mesh.
These terms are - for example - used in the 
Selection
toolbar.
Supermesh
The supermesh is a set of polygons and possibly
lines and points that is used as the basis for mesh
generation (using the 
Meshing
panel). To set up the supermesh, tools in the Mesh-Editor toolbar are applied.
For unstructured meshing in 3D, a 3D version of
supermesh can be used. This cannot be edited via the
Mesh-Editor toolbar, but is generated
either by using the New
model dialog or by converting maps from within the Maps panel.
Mesh
The finite-element mesh includes all the elements
with their nodes and provides the spatial discretization
that is a precondition for applying the finite-element method. The mesh
is generated before populating the FEFLOW model with data by using the
Meshing
panel.
Node
The nodes are the corner points of triangular or quadrilateral (2D) or prismatic (3D) elements. They carry the primary variables hydraulic head, mass concentration and temperature and within the finite-element discretization they are therefore the locations where simulation results are calculated. Nodes also carry boundary condition and constraint information.
In 3D models, nodes carry elevation information and hereby form the shape of the slices and layer tops/bottoms in z direction.
Element
Triangular or quadrilateral (2D) or prismatic (3D) elements subdivide the model area (2D) or 3D domain into discrete parts. They carry all material-property information.
Layer
In three-dimensional models, elements are organized on layers. On each layer, there is an identical number of elements with the same location in X and Y. Thus, in z direction at each point of the model domain in X-Y, there is a number of stacked elements corresponding to the number of layers in the model. Layers need to be continuous over the entire model area.
Slice
In three-dimensional models, nodes are organized on slices. On each slice, there is an identical number of nodes with identical locations in X and Y. Thus, in z direction at each point of the model domain in X-Y, there is an identical number slices. Slices need to be continuous over the entire model area.
Slice Edge
The term Slice Edge describes the edges of elements, in 3D models edges of elements on a slice. Thus slice edges always connect two neighboring nodes of an element, in 3D models on a slice.
Slice edges may carry one-dimensional Discrete Features.
Join Edge
In contrast to slice edges, join edges denominate element edges in z direction, connecting nodes at the same X-Y location on two neighboring slices. The join edge always spans over one layer and exists in 3D models only.
Join edges may carry one-dimensional Discrete Features, Multilayer Wells and Borehole Heat Exchangers.
Edge
From FEFLOW 7, FEFLOW does no longer distinguish between slice edges and join edges, and instead uses Edge as the terminology. Legacy models may still contain slice and join edge selections, and Discrete Features based on them, but it is recommended to only use edges for new setups.
Edges may carry one-dimensional Discrete Features, Multilayer Wells and Borehole Heat Exchangers.
Slice Face
The term Slice Face describes the faces of elements, in 3D models faces of elements on a slice.
Slice faces may carry two-dimensional Discrete Features.
Join Face
In contrast to slice faces, join edges denominate element faces in z direction, connecting two neighboring nodes at the same X-Y location to nodes at an identical X-Y location on the neighboring slice. The join face always spans over one layer and exists in 3D models only.
Join faces may carry two-dimensional Discrete Features.
Face
From FEFLOW 7, FEFLOW does no longer distinguish between slice faces and join faces, and instead uses Edge as the terminology. Legacy models may still contain slice and join edge selections, and Discrete Features based on them, but it is recommended to only use edges for new setups. Faces may carry two-dimensional Discrete Features.
Arbitrary Node Path
This term refers to an arbitrary connection of a number of nodes in the mesh. Arbitrary node paths may carry one-dimensional Discrete Features that are only connected to the nodes linked by the node path.
Discrete Features
This term refers to an arbitrary geometry, which has been used to create discrete feature elements. A fracture can be a edge, slice-edge, join-edge, face, slice-face and join-face.