What does "difficulty" refer to in the chain specification, if actual difficulty is determined by hashrate?
I know that "difficulty" went down after the ETH/ETC fork, but why then is difficulty in the chain spec at all?
What does "difficulty" refer to in the chain specification, if actual difficulty is determined by hashrate?
By this I'll assume you mean the difficulty stated in the genesis block (as per the Genesis subsection of the Chain Spec).
Values set in the genesis block are default starting values, which are subject to change as the chain and network grow. (I don't know why the particular value in the genesis file was chosen. Perhaps arbitrary, perhaps a trade-off between the expected starting network size or hash rate, and some other factors?)
As a network grows in size and its hash rate increases, the time between blocks being mined will, on average, decrease.
If the time between blocks decreases, the difficulty adjustment algorithm kicks in and increases the difficulty in an attempt to maintain a static block time.
See: