Inspiratory capacity is the maximum amount of air a person can inhale starting from a normal resting exhale, combining a normal tidal breath with all remaining inspiratory reserve.
IC is everything above the resting volume — it shrinks as hyperinflation raises FRC.
It's sometimes tracked in COPD to assess hyperinflation, since a falling IC relative to TLC reflects worsening air trapping — the resting volume (FRC) creeps up and leaves less room to inhale.
Roughly 3.5 L in an average adult — the maximum that can be inhaled starting from a normal resting exhale.
The tidal volume of a normal breath plus the inspiratory reserve volume. Equivalently, it's total lung capacity minus functional residual capacity.
Air trapping raises FRC (the resting volume), so the lungs start each breath already partly inflated, leaving less capacity to breathe in.