Authentic means that something is real, verified, or genuine. It is an adjective, so it is used to describe a noun. Another meaning implies that something is done to resemble an original, according to Merriam-Webster's dictionary. An example would be a meal that is made in the style of a popular Chinese dish.
Authentic has another, less-common definition and is used in the field of music. Authentic notes refer to a note and those up to and including those an octave higher. This is most commonly used with church music and is not typically found in regular conversations or writings.
