An IOI is a non-binding letter prepared by the buyer to the seller expressing a genuine interest in acquiring the company, but the issuer hasn’t yet had the opportunity to review sufficient data (due diligence) regarding the company. An IOI will offer an approximate price range. An IOI may be issued in advance of an LOI if the buyer is really serious, there are other buyers interested, and there is a sense of urgency to getting some information into the sellers’ hands. An IOI will also give you an idea of who is serious and who is not.
Glossary Index / Indication of Interest (IOI) or Expression of Interest (EOI)