3 Answers

The Rules of Golf do not prohibit a player from using headphones, provided they do not communicate information on the conditions (such as weather) which are relevant to his play or otherwise assist the player in his play. Please refer to Rule 14-3, Decision 14-3/16 and the penalty statement under Rule 14-3. Additionally, the Rules of Golf do not prohibit a player from using earplugs, provided it does not assist the player in his play - (Rule 14-3). Finally, a prudent player would avoid the appearance of any possible breach of the Rules. The decision on whether a breach has occurred needs to be made by a rules official or other member of a Committee on a case by case basis, taking all of the circumstances into consideration.

Listening to music on headphones or any other way, on a golf course, would always be considered very bad manners. The etiquette of playing golf is high on the priority list. You might want to read a book on golf etiquette so that other golfers will enjoy playing with you. Otherwise, it won't be too likely.

I don't know what the "official rule" is. I do however, know golfers!

 United States Golf Association Rules:

Rule 14-3
Wearing Headphones or Earplugs During Stipulated Round
Q. May I wear headphones or earplugs while playing in the state amateur?
A.
The use of headphones or earplugs to eliminate noise or other distractions is prohibited under Rule 14-3.
Decision 14-3/16 covers listening to music or some other broadcast during a round. Here is the text of that Decision:
Rule 14-3a states that a player may not use any artificial device or unusual equipment that “might assist him making a stroke or in his play.” Listening to music or a broadcast while making a stroke or for a prolonged period might assist the player in his play, for example, by eliminating distractions or promoting a good tempo. Therefore, the use of an artificial device to listen to music or a broadcast, whether or not through headphones, while making a stroke or for a prolonged period of time during a stipulate round is a breach of Rule 14-3. However, it would not be a breach of Rule 14-3 for a player to listen to a device briefly, for example, to obtain the results of another sporting event or traffic information, while walking between the putting green of one hole and the teeing ground of another hole.
There is no restriction on listening to music or other broadcasts while practicing (whether on the practice ground or on the golf course, and whether by oneself or while playing with others), although club rules and disciplinary codes could apply in such circumstances.