Intellectual property cores are types of CPUs primarily used in embedded and mobile platforms, mainly made by companies like ARM or MIPS. The idea with IP cores is that they’re intended for integration with other logic, including application-specific processors (like GPUs, IO interfaces, memory interfaces), then combined for a generally better processor for a specific purpose.
The ARM Cortex-A9 in the DE1-SoC is an IP core, but a chip that incorporates it (like a Snapdragon CPU) adds extra logic.
Most vendors that use/sell ARM chips (Qualcomm, Apple) use ARM IP cores and add extra stuff.