In a mathematical and conceptual sense, a two-dimensional object is considered to have only length and width, with no measurable thickness. However, in the physical world, it is practically impossible to have a perfectly two-dimensional object due to various factors such as atomic structure and quantum effects.
In reality, even objects that are extremely thin, such as a sheet of paper or a single layer of atoms in graphene, still possess some degree of thickness. These objects may approach two-dimensionality in terms of their behavior and properties, but they will still have a finite thickness when measured.
The notion of dimensionality is often more of a continuum rather than an absolute distinction. Objects can exhibit varying degrees of dimensionality, with some being closer to two-dimensional than others. For practical purposes, an object is often considered two-dimensional when its thickness or height is negligible compared to its length and width, and its behavior can be accurately described using two-dimensional models or theories. However, it's important to note that in the physical world, true two-dimensionality is purely theoretical.