"Interannual variations" refers to changes or differences that occur from one year to another in a repetitive pattern. It describes fluctuations or fluctuations that happen annually over multiple years. Full definition
Wong, S., and W. - C. Wang, 2003: Tropical - extratropical connection in interannual variation of the tropopause: Comparison between NCEP / NCAR reanalysis and an atmospheric general circulation model. (pa.op.dlr.de)
«A Comparison of Modeled and Observed Relationships between Interannual Variations of Water Vapor and Temperature.» (history.aip.org)
al (2013) found a robust relationship between the efficiency of carbon release into the atmosphere with interannual variations of tropical temperature and the weakening in carbon storage under global warming. (climate-dynamics.org)