What is Takalluf (overburdening oneself) or Tanattu' (extremism/rigorism)?

"Takalluf" (over-elaboration) and "tanattu'" (excessive meticulousness) are terms applied to exaggeration and exceeding the limit in speech and action. For this reason, the Prophet, peace and blessings be upon him, said: "Ruined are those who over-elaborate," repeating it three times.