verb

• (transitive) To join or unite (e.g. one thing to another, or as several particulars) so as to increase the number, augment the quantity, or enlarge the magnitude, or so as to form into one aggregate.
• (transitive) To combine elements of (something) into one quantity.
  "to add a column of numbers"
• (transitive) To give by way of increased possession (to someone); to bestow (on).
  "The Lord shall add to me another son."
• (transitive) To append (e.g. a statement); to say further information; to add on.
  "He added that he would willingly consent to the entire abolition of the tax"

noun

• (radio) The addition of a song to a station's playlist.
  "In a typical week, 10 to 15 songs may be up for consideration as “adds” of new songs for the station's playlist."
• (computer science) An act or instance of adding.
  "List the number of adds and multiplies for each of the forms (6) , (7), and (8)."
• (video games) An additional enemy that joins a fight after the primary target.
  "When the player has fought the boss for one minute, two adds will arrive from the back and must be dealt with."

noun

• (pathology) Initialism of attention deficit disorder.
• (insurance) Initialism of accidental death and dismemberment.
  "Although not sought by QuesTech, the dismemberment portion of the policy was nonetheless issued as an integral part of Hartford’s standard ADD policy."
• (sound engineering) A designation on prerecorded compact discs indicating that the contents were recorded in analog but mixed and mastered in digital.