Resistance tells you how much a component opposes DC (direct current) — it's a single number in ohms. Impedance tells you how much it opposes AC (alternating current) at a specific frequency — and it changes with frequency.
An inductor has low impedance at low frequencies and high impedance at high frequencies (it resists changes in current). A capacitor is the opposite: high impedance at low frequencies, low at high (it resists changes in voltage). A resistor has the same impedance at all frequencies.
When you combine these in a circuit, the total impedance at any given frequency determines how much current flows and where the energy goes. At resonance, the impedance of the inductor and capacitor cancel each other out, and the circuit's impedance reaches a peak (in a parallel LC) or a minimum (in a series LC).
Why it matters for the experiments
Most Open Energy experiments involve measuring impedance across a frequency sweep using a NanoVNA. The shape of the impedance curve tells you everything: where the resonance is, how sharp it is (Q factor), and how the component's behavior changes with frequency.
When the blog posts and experiment templates talk about "impedance peak at resonance," this is what they mean: the frequency where the system's opposition to current flow is highest, which is also where energy storage is most efficient.