What is the meaning of the UNPREDICTABLE in random function?

Linguistically I understand the meaning of unpredictable. But, during this time I often find the word predictable in some cases. I usually find these words if I enter an area with several topics, for example:

1. Math.random vs crypto.getRandomValues in Javascript
2. Random vs Secure Random numbers
3. Etc

So what exactly does unpredictable mean in random functions? Then what are the conditions for a random function to be called "unpredictable random function"?