The answer is TODAY
An adverb is a word or set of words that modifies a verb, an adjective, a clause, another adverb, or a phrase, meaning that it can describe how, where, or when an action took place. There are many types of adverbs, and "Today" is an adverb of time as it tells us WHEN something happens, and they are usually placed at the end or at the beginning of the sentence.
Other adverbs of time are now, yesterday, last year, tomorrow, etc.