part-of-speech disambiguation - determining the correct Part of Speech (PoS) tag of a word with several possible PoS tags. HHMs for PoS can be used to solve this problem
word sense disambiguation - determining the correct meaning/sense of a homonym (a word with several different meanings)
syntactic disambiguation - determining the correct parse tree among several possible trees. can be solved with probabilistic parsing
speech act interpretation - determining whether sentence is a question or statement