Mesh
A mesh is a 3D model's surface represented as a network of connected vertices, edges, and faces — usually triangles.
A mesh defines the shape of a 3D object as a web of points (vertices) joined into faces. Most 3D-printable models are triangle meshes, and the density of those triangles controls how smooth or faceted the surface appears.
A mesh must be "watertight" — fully enclosed with no holes or gaps — to print correctly. Repairing non-manifold or broken meshes is a common step before slicing a downloaded model.
STL
STL is a common 3D file format that describes an object's surface as a mesh of triangles, used as input for 3D printing.
Slicer
A slicer is software that converts a 3D model into the layer-by-layer instructions a 3D printer follows to build the object.
FDM
FDM is a 3D printing method that builds objects layer by layer by extruding melted thermoplastic filament through a heated nozzle.
Put Mesh to work this week.
Knowing the term is step one. The business kits ship the systems and templates that turn concepts like this into a running operation.