A transition to zero resistance
A very good ordinary conductor still dissipates energy through resistance. A superconducting transition produces a different state in which suitable loops can sustain current. Early low-temperature measurements of mercury revealed a transition rather than an indefinitely smooth improvement in ordinary metallic conductivity.
The Meissner effect
The Meissner effect involves expulsion of magnetic field under suitable conditions and is not implied by zero resistance alone. Type-II superconductors can enter a mixed state permitting localized flux penetration over a field range, allowing useful superconducting behaviour in stronger magnetic fields.
A collective electronic state
BCS theory explains conventional superconductivity through paired electrons and a collective quantum state. Pairing is not ordinary permanent molecular bonding, and the state depends on material conditions. A simplified conventional picture should not be assumed to explain every superconducting material in the same way.
Critical conditions and cooling
Temperature, applied field and current can destroy superconductivity above critical conditions. Superconducting magnets serve particle accelerators, but refrigeration and supporting systems still consume energy. Zero resistance is a property of the material state, not a claim that the whole installation runs without power or operates at room temperature.