Ocarina Items is the term used to describe a glitch which allows link to use and play other items as if they were the ocarina. This leads to the ability to play songs in places where the regular ocarina item is unusable, or in situations where the player does not have the regular ocarina (such as if it has been overwritten using bottle duplication).
There are various methods to perform the glitch, all found in Ocarina of time and tested out in Majora's Mask.
Note: The bottle must be out and in link's hands when the ESS is performed. Items that work for the glitch are those which link will actually take out and hold or use, such as bow, bombs, sword, zora fins, deku bubble, hookshot, etc.
If done correctly, link should pull out the item and start playing it as if it were an ocarina. This method can be used with masks and items of 0 item count as a form of bottle duplication.
Note: Link's arms should be coming down at the same time as the item is used. This is a 1 frame trick. Cutscene items include: transformation masks, any full bottle, title deeds and other trade items.
If performed correctly, Link's arms should come down and he should be playing an invisible ocarina.
The ESS method of this trick can be used with zora fins in order to use the ocarina underwater. This is useful in pinnacle rock, where the last egg can be caught and then instantly used for the Ocarina Items glitch in order to soar away.