What is Inductor and inductance?

An inductor is a coil of wire: its current threads its own turns with a magnetic field (Chapter 15); whenever it changes, a voltage appears across the coil:

The constant $L$ is the inductance, in henries ($\mathrm{H}$): $1\,\mathrm{H} = 1\,\mathrm{V}\,\mathrm{s}/\mathrm{A}$.