An Integral field spectrograph is a spectrograph equipped with an integral field unit (IFU). In this method,
the light from each pixel of the detector is fed into a spectrograph, which generates a spectrum for each individual pixel. This muliplexing
capability allows one to obtain spectra of every single pixel of an image simultaneously. This is a game changer in terms of how astropysical observations are carried out.
Please look here for a nice description of how IFUs work.
In recent years, several integral field spectrographs which cover large fields of view have come online (e.g. VLT/MUSE, Keck/KCWI) and several (Llama/Magellan) are coming online in the near future.
I am heavily involved with IFU observations and software development to get the best out of these amazing instruments.
I am leading several efforts to use these IFUs and study the gas flow around galaxies in 3D.