What is Redshift and blueshift?

Example 23.16 (Weighing a star’s escape)

In the spectrum of the bright star Vega, the hydrogen line of laboratory wavelength $656.30\,\mathrm{nm}$ is measured at $656.27\,\mathrm{nm}$: $\Delta\lambda = -0.03\,\mathrm{nm}$, a blueshift, so Vega approaches at $v_r = c\,|\Delta\lambda|/\lambda \approx 1.4 \times 10^{4}\,\mathrm{m}/\mathrm{s}$ — $14\,\mathrm{km}/\mathrm{s}$, read off a shift of one part in twenty thousand.