Two words that sound interchangeable, are used interchangeably by almost everyone including people who work at brokerages, and mean completely different things to the IRS.
Rollover. Transfer.
Pick the wrong one and you can trigger a tax bill on money you never spent, blow a rule you did not know existed, and discover the mistake fourteen months later when a tax form arrives.
Pick the right one and nothing happens at all, which is exactly what you want when moving retirement money.
Here is the difference, in plain language, with the traps marked.