Fronted Adverbials

What is a fronted adverbial? 

An adverbial is a word, phrase or clause that is used, like an adverb, to modify a verb or a clause. Adverbs can be used as adverbials, but many other types of words, phrases and clauses can be used in this way. When adverbials are used at the beginning of a sentence, they are called ‘fronted adverbials’.