* Bound morphemes: These are units of meaning that cannot stand alone as words and must be attached to other morphemes. They can be prefixes, suffixes, or infixes. Examples include the prefix "un-" in "unhappy" or the suffix "-ing" in "walking."
* Clitics: These are words that are phonologically attached to another word, but retain their own meaning. They can be prefixes, suffixes, or enclitics (attached to the end of a word). For example, "n't" in "can't" is a clitic.
It's possible the term "semi-affixes" is used informally to describe a particular linguistic phenomenon, but it's not a recognized term in standard linguistic theory.
If you can provide more context about where you encountered the term, I might be able to give you a more specific answer.