I would like to know the meaning of the Hadeeth in which the Prophet, sallallaahu ‘alayhi wa sallam (may Allaah exalt his mention), forbade:
1- Selling silver for silver except like for like, without any difference in quantities,
2- Selling gold or silver that is not present at the moment of exchange, for gold or silver that is present.
[Al-Bukhaari & Muslim]

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The Hadeeth you mentioned refers to the prohibition of selling gold for gold except like for like, without any difference in quantities (weight), even if there is any difference in price for any reason, for example, different market demands or because one kind is 18k gold and another is 24k gold. The same ruling applies to selling silver for silver.

The Hadeeth also prohibits selling gold for gold; silver for silver, or silver for gold if both items are not present at the moment of exchange. 

The Shaafi‘i  scholar, Ibn Hajar   stated that it is prohibited for someone who owns gold or silver to sell them if they are not actually present with him at the time of sale. Naturally, the same ruling applies to anyone who does not own the transacted silver or gold in the first place.

Allaah Knows best.