What is global digital asset exchange (GDAX)?

Could you elaborate on what the Global Digital Asset Exchange, or GDAX, entails? From my understanding, it was initially a trading platform offered by Coinbase, renamed from the original Coinbase Exchange. It seems to have provided a centralized marketplace for digital asset investors, supporting trading pairs beyond just Bitcoin, such as Bitcoin-Ether and Bitcoin-fiat currency pairs. Additionally, it offered professional investors access to various APIs for market information and asset management. However, I've heard that Coinbase has since rebranded GDAX to Coinbase Pro, yet the underlying services and functionalities remain largely the same. Could you elaborate further on the services offered, the target audience, and any significant changes that have occurred since its inception?