What is the meaning of the "Registered" part in "Registered Retirement Savings Plan"? What is an example of an unregistered savings plan?
In a nutshell, the "Registered" part of RRSP means it is a special type of account (special in that it has tax advantages that non-registered accounts don't get) and, more specifically, that the government sanctions and permits it and, furthermore, that administrators working on the government's behalf to administer registered plans must follow the rules that are set out for such plans.
Here's a definitive source: Canada Revenue Agency - Registered Retirement Savings Plan (RRSP).
An RRSP is a retirement plan that we* register and that you or your spouse or common-law partner establish and contribute to. Deductible RRSP contributions can be used to reduce your tax.
* The "we" being Canada Revenue Agency.
Tax Free Savings Accounts (TFSA) are another example of a registered plan, even though it doesn't have the word "Registered" in the name. Go figure.
You'll find the TFSA listed under a list of registered plan types at Canada Revenue Agency - Tax - Registered plans administrators, alongside other kinds you probably didn't know existed.
Note that registered plans themselves are not administered by the Canada Revenue Agency: CRA permits banks, brokers, trust companies, insurance companies, etc. to take care of all that, and those who offer registered plans must follow CRA's rules, including informing CRA of the plans that get established.
Finally, a "non-registered" plan (not unregistered) is simply a regular investment or savings account. There's nothing special about it. It's unremarkable. You earn money in one, and you owe tax. No sheltering, no deductions.