Trying to understand what is needed to make HCLG.fst file.
monophones - just means phone without context
triphones - means a sequence of 3 phones, i.e. left-context/phone/right-context
In linguistics, a triphone is a sequence of three consecutive phonemes. Triphones are useful in models of natural language processing where they are used to establish the various contexts in which a phoneme can occur in a particular natural language.[wikipedia https://en.wikipedia.org/wiki/Triphone]