A hash pointer is a data structure that turns out to be useful in many of the systems that we consider. A hash pointer is simply a pointer to where some information is stored together with a cryptographic hash of the information. Whereas a regular pointer gives you a way to retrieve the information, a hash pointer also allows you to verify the that the information hasn't changed. 1^ A hash pointer is a pointer to where data is stored together with a cryptographic hash of the value of this data at some fixed point in time.
We can use hash pointers to build all kinds of data structures. Intuitively, we can take a familiar data structure that uses pointers, such as a linked list or a binary search tree, and implement it with hash pointers instead of ordinary pointers, as we normally would.
Narayanan, Arvind, et al. (2017). Bitcoin and Cryptocurrency Technologies. United States: Princeton Press