In general relativity, light moving away from a mass or other source of gravity experiences a shift towards lower frequencies. This is called the gravitational redshift; on the other hand, light falling towards a mass is blueshifted. Both effects together are called the gravitational frequency shift. The gravitational redshift is closely related to gravitational time dilation.
Information about an astrophysical application of this effect can be found in the spotlight text Gravitational redshift and White Dwarf stars.