Spectral Resolution is a measure of a Spectrograph's ability to distinguish features in the spectrum, typically noted as ΔΛ, meaning the smallest division in Wavelengths that the spectrograph can distinguish.
The Resolving Power is defined as:
λ R = —— Δλ
Cross Dispersion Spectrograph
Double-Line Spectroscopic Binary
European Extremely Large Telescope (E-ELT)
Gran Telescopio Canarias (GTC)