Yes! There is a big difference!
Sim Network unlock Pin is quickly misinterpreted as the 4 digit PIN number connected with your SIM card, however this is not the case. The SIM pin is known as the SIM PUK. However, the Sim Network unlock Pin is in fact the unlock code to network unlock your phone. This is frequently called, the Network Unlock Code, Network Control Secret (NCK), Master Unlock as well as other terms. I know it can be confusing, but the word of thumb is: if it contains the work NETWORK, then this is referring to the code to remove the network restrictions from the phone.