Bottle Duplication (commonly referred to as "bottle dupe" or "duping") is a technique that allows you to replace items in Link's inventory with a bottle. This may seem useless at first, but it is very helpful when collecting the Zora Eggs in a speedrun, since you then only have to collect one legitimate bottle. It is also a prerequisite to performing Bottle Adventure.
Note: The bottle must be out and in link's hands when the ESS is performed. Those items stated above are the only ones which work.
If performed correctly, either a 0 item count sound will play or link will put on a mask, followed by him emptying out the bottle. After this animation has played, the item or mask will be replaced with an empty bottle.
† You can mash the start button here if you find it easier
†† Again, mashing the C button is also an option
This video demostrates all 3 methods described above in order:
The first method, the ESS method is the easiest and most convenient to perform if bottles are required, as it is a quick and easy method which can be performed anywhere, however only a limited number of items may be duplicated over this way. The curiosity shop method is useful as not only can any item be duplicated over, but rupees are gained each time the trick is performed and the item isn't used up (up to 200 rupees if a valuable item is used). This makes it a great source of rupees, especially for 100% speedruns of the game in which rupees are required for the bank heart piece.
Of the two Curiosity Shop methods, the first method is a general method that will always work. The second method can only be used if the C-button item in question can be used inside the shop. This means it is mostly limited to duplicating over masks and other non-offensive items like the Ocarina or the Pictobox whereas the first method may duplicate over any item which can be equipped to the C-buttons.
Using collection delay makes the curiosity shop version of the trick extremely easy, but requires at least two bottles.
Using the same method as the Curiosity Shop versions of the trick, it is also possible to duplicate bottles in the Magic Hags' Potion Shop by depositing a Magic Mushroom. The trick works in the exact same way, but the downside is that it requires the Mask of Scents.