If a suggestion, plan, rule, etc. is carved in stone, it cannot be changed.

無法改變的;鐵板釘釘?shù)?/p>

These proposals are for discussion, they're not carved in stone.

這些提議是供討論的，并非不可更改。

The deal isn't yet carved in stone, but we're confident it will go ahead as hoped.

這筆交易還不是板上釘釘?shù)?，但我們相信它?huì)如預(yù)期進(jìn)行下去。