Offset

From NMR Wiki

Offset (Ω, omega; majuscule ) is the difference resulting from substration of the rotating frame frequency (ω_rot.frame, omega; minuscule) taken from the Larmor frequencey (ω₀). Then, Ω is given by the expression: [Ω = ω₀ − ω_rot.frame]. The units for offset are in hertz.