The Blender Lattice (sometimes "deformation cage" in other software) is "a three-dimensional non-renderable grid of vertices" that is mainly used to deformation the object it controls with a Lattice Modifier. Use this tag for questions about the lattice and the lattice modifier.
The Blender manual describes the Lattice thusly:
A lattice consists of a three-dimensional non-renderable grid of vertices. Its main use is to apply a deformation to the object it controls with a Lattice Modifier. If the object is parented with Lattice Deform a Lattice Modifier is automatically applied.
Use this tag for questions about the lattice and the lattice modifier.