Conjunctive adverbs are adverbs that act as a transition between complete ideas. They normally show comparison, contrast, cause-effect, sequence, or other relationships. They usually occur between independent clauses or sentences.
The following words are common conjunctive adverbs:
accordingly, again, also, besides consequently, finally, furthermore, however, indeed, moreover, nevertheless, otherwise, then, therefore, and thus.
See Commas with Interrupting Expressions and Semicolons with Clauses for information on punctuating and using conjunctive adverbs.