A system-on-chip (SoC) is an integrated circuit (IC) that integrates many components or functions like multi-core processor, memory blocks, and analog/external interfaces into a single chip.
Apple A9 SoC processor
The Apple A9 is a SoC, designed by Apple Inc, appeared in the iPhone 6S and 6S Plus which were introduced on September 9, 2015. The A9 features an Apple-designed 64-bit 1.85 GHz ARMv8-A dual-core CPU called Twister and a GPU IMG PowerVR GT7600. The A9 in the iPhone 6S has 2 GB of LPDDR4 RAM included in the package (System-in-Package, SiP). Apple A9 chips are fabricated by two companies: Samsung and TSMC.
SoC vs. SiP