What is ftdi diet stand for?

I reckon there might be a small typo in your question. It's usually 'FTD', not 'FTDI'. That's a very easy mistake to make!

FTD stands for Frontotemporal Dementia. It is a type of brain condition. So, the 'FTD diet' isn't really one single diet plan. It is more about the best food advice for people who have this illness. It helps to manage certain symptoms. Things like big changes in appetite or problems with swallowing. It's all about helping them eat safely and stay healthy. Cheers.