IF is a company that administers its own currency for public use. They function like a bank with more power. The currency they've established is simply called IFCs. IFCs are worth the number of IFCs currently held by IF's central bank.
The public can buy IFCs directly or invest into the company. Investing enough grants IFCs that are held by IF and raises the value of all IFCs by one. Exchange rates between Credits, Photons, GOTs, and IFCs are highly complex and change constantly. The general idea is the public invests in various currencies, IFCs go up in value, then people rely on exchanging IFCs as a speculative market that 'can only go up in value'.
For the most part the currency is actually spent/exchanged by large freight companies. They can exchange huge amounts of wealth but only use a handful of IFCs. Most small companies' entire worth won't even reach the value of a single IFCs. Large companies keep huge numbers of IFCs invested into IF which keeps their individual value high.