This article discusses the principal problems of delimiting the scope of adverbs and their classification in terms of lexicology, lexicography and natural language processing, with a view to making the exhaustive lexical database for adverbs as well as to developing the description models which lead to the construction of the lexicon. Our discussion is not limited to the adverbs in traditional sense, but extended to the mono-/poly lexical words which can be considered as adverbials morphologically, syntactically and lexicologically. For instance, N+postposition(distributionally very limited), limited and/or productive inflectional forms of verbs and adjectives, and fixed forms of phrases and sentences which we consider as compound adverbs. To support our explanation, the morphological and syntactic properties of adverbs are discussed with typological and language universal point of view. Semantic classification is not included in this article because we think it can not be made rigorously without delimiting and analyzing possible various forms of adverbs(and adverbials) and their syntactic functions.