valuable things offered or given to people who do not appreciate them明珠暗投，对牛弹琴，把贵重的东西送给不识货的人
柯林斯高阶英汉双解学习词典释义
N-COUNT
珍珠
A pearl is a hard round object which is shiny and creamy white in colour. Pearls grow inside the shell of an oyster and are used for making expensive jewellery.
If you say that someone is casting pearls before swine, you mean that they are wasting their time by offering something that is helpful or valuable to someone who does not appreciate or understand it.