Here's a breakdown:
* Infix: An infix is a morpheme that is inserted within another morpheme, often changing the meaning or grammatical function of the original word.
* Example: In some languages, like Tagalog, an infix can be used to indicate past tense. The word "kain" (to eat) becomes "kumain" (ate) by inserting the infix "-um-" between the first and second letters.
* Interfix: This term doesn't exist in standard English grammatical terminology. It might be a misunderstanding or an invented term.
Key takeaway: While infixes are a phenomenon found in some languages, they are not a feature of standard English grammar.