The IFS (Integrated Forecasting System) is a global data assimilation and forecasting system, developed by ECMWF. Initially the IFS was developed only for weather forecasting, but it evolved into a generic global model and now includes the modelling of the atmospheric composition (greenhouse gases, aerosols, and chemical species). The atmospheric composition outputs from the IFS are released as CAMS Global near-real-time data.
As of May 2017 the horizontal resolution of the CAMS Global data is ~40 km (T511L60). Output data is available at a 3-hour intervals.
Until about 2017 the term C-IFS (Composition Integrated Forecasting System) was also in use, referring to the part of the IFS designed to produce atmospheric composition data (as opposed to weather data). However, the IFS is in fact a single system, so the term C-IFS should not be used.
For further details see the ECMWF pages on modelling and prediction and this paper:
Flemming, J., Huijnen, V., Arteta, J., Bechtold, P., Beljaars, A. Blechschmidt, A.-M., Diamantakis, M., Engelen, R. J., Gaudel, A., Inness, A., Jones, L., Josse, B., Katragkou, E., Marecal, V., Peuch, V.-H., Richter, A., Schultz, M. G., Stein, O., and Tsikerdekis, A.: Tropospheric chemistry in the Integrated Forecasting System of ECMWF, Geosci. Model Dev., 8, 975-1003, doi:10.5194/gmd-8-975-2015, 2015.