From the comments at: https://money.stackexchange.com/a/85769/4522
One poster called an IRA an:
Individual Retirement Account
Another stated it was an:
Individual Retirement Arrangement
What does the IRA abbreviation actually stand for?
It means both.
However, in the tax code, they are called Individual Retirement Accounts (Title 26, Section 408).
In my experience, you will see it described as Individual Retirement Accounts nearly everywhere you look except for the IRS publications.
They all refer to the same thing, and there really is no distinction between the two. I believe that the IRS changed the name to Arrangement because an IRA can encompass a variety of assets, some of which are difficult to describe as "accounts."
From the first sentence of the IRS publication 590-A on IRAs:
This publication discusses contributions to individual retirement arrangements (IRAs).
IRA : individual retirement account is an investing tool used by individuals to earn and designate funds for retirement savings. Also Known as Individual Retirement Arrangements : Sometimes referred to as individual retirement arrangements because IRAs can consist of a range of financial products such as stocks, bonds or mutual funds.
Reference : IRA - Investopedia
It means both, because the Individual Retirement Account implements an Individual Retirement Arrangement.
EDIT: this should not be construed to mean that this is a person's only implementation of an Arrangement.