Step 1: Concept
Teflon is the brand name for Polytetrafluoroethylene (PTFE).
Step 2: Meaning
Polymers are named after their monomers. "Poly" + "tetrafluoroethylene" indicates the starting material.
Step 3: Analysis
Tetrafluoroethylene consists of an ethylene unit where all four hydrogen atoms are replaced by fluorine atoms ($F_{2}C=CF_{2}$).
Step 4: Conclusion
Thus, the monomer of Teflon is tetrafluoroethylene, represented by option D.
Final Answer: (D)