What are the best resources for learning banking terminology, processes, and business rules, especially in corporate banking?

There is no easy answer for this. Depending on where in the world you are, the answer will vary.

Some important pointers for you.

• You cannot short-circuit the learning time.
• It does take time to absorb it all. Think of it as no different from say trying to understand baking, carpentry, automobile engineering, etc. It works at its own pace.
• Spend as much time as you can with Bankers. They are your friends. Learn one or two things from them every time you meet up with them. When in doubt, call them up and ask. Remember, their time is precious, so be precise.
• Quora is a great resource to understand a lot in the banking space. So spend generous amount of time here.
• Look for workshops in the payments and banking space. Sign-up for them and attend them. Even if you walk away learning one thing, that is good enough. These workshops are a great way to network with people in the banking/payments space.
• Set aside one-hour at least for your learning. Read this excellent post by Mike Townsend: How To Integrate 1 Hour "Learning Sprints" Into Your Life
• Understanding definitions and acronyms is important, but do note, there can be entire ecosystem hiding behind a single word. Take time to learn and understand. Definitions may vary from territory to territory. Always consult multiple sources to get a better grasp on a definition and its explanation.
• Search for white-papers by various banking/payment companies. They go deep into explaining various concepts. These papers are difficult to read the first time around. But then, this is what you asked for.
• Reports: Perhaps the most important aspect of learning are reading and comprehending reports. Reports can seem very thick and boring to read, but they are worth their weight in gold.
• Read the circulars and manuals of your Central Bank. I cannot recommend a better source for learning.
• When in doubt, ask questions! Be patient with answers.
• YouTube: Watch as many finance, banking and payments related videos you can.
• Podcasts are also a fantastic way of learning, for some it is a subliminal way of learning. Shameless plug, but a podcast called Around The Coin by Brian Roemmele, Mike Townsend and myself, explains a lot. It is a weekly podcast and you can access all the archives here: Around The Coin