Cryptographic primitives are well-established, low level cryptographic algorithms that are frequently used to build cryptographic protocols. Examples of cryptographic primitives: one-way hash functions and encryption functions.
If it is said that a cryptographic primitive takes atleast X number of computational operations to break, and it can be broken by a lower number of operations, that cryptographic primitive is termed to be un-reliable. In that case, every cryptographic function based on that primitive becomes vulnerable.