Conjunctive Adverb
The following are conjunctive adverbs: however, consequently, therefore, thus, hence, furthermore, moreover, afterward, indeed, othersie, in fact, that is.  When one of these words is used to connect two sentences, a semicolon comes before the conjunctive adverb and a comma comes after it.  Some of these words can be used as transitional words or phrases.  In that case they do not connect two sentences and are set off with commas.  Example:  Conjunctive adverb - The students are going to the library; however, their time there is limited.  Transitional phrase - The students, however, are going to the library.