Impedance describes electrical load
Impedance, measured in ohms, tells you how much a headphone resists the signal coming from your source. Higher impedance models often need more voltage to reach the same volume. Lower impedance models are easier to drive loudly, but they can also expose amplifier noise or output impedance issues more readily.
High impedance does not automatically mean better sound
Some classic studio headphones use 250 or 300 ohm drivers, but that does not make high impedance a quality badge on its own. Driver tuning, sensitivity, distortion behavior, and fit matter much more. The spec only becomes useful when you pair the headphone with a real source device.
Look at sensitivity too
Two headphones can share the same impedance and still behave very differently because their sensitivity differs. One might get loud from a phone dongle while the other feels restrained. This is why volume complaints are usually solved by reading both specs together, not just one.
If a new pair sounds weak or compressed from a phone but opens up on a better source, the issue may be power headroom rather than tuning.