In the following sensor datasheet (https://github.com/rellimmot/Sony-IMX219-Raspberry-Pi-V2-CMOS/blob/master/IMX219PQH5_Module_Design_Reference_Manual_ver2.2_140425.pdf), it details the supply voltages for the major components on page 13. There's a supply voltage for a component labeled "IF". What does "IF" stand for?
It is really not easy to find information about this module, and there seems to be no datasheet available online! Only product brief and some fragmented data. But here's the answer to your question, however for slightly different model
Power supply Analog 2.5V Digital 1.1V Interface 1.8V
Here's one more. Funny enough lack of information about product should play bad joke with Sony.
No way to know without asking the author, it's non-standard.
Could be "Imaging Function", could be "InterFace", and given that datasheet is slapped together with lots of rough edges and they use the word "Share" when they mean "shear", it could also be a mistake, a mistranslation or a non-English word.