A Backdoor is a post-tax contribution to a Trad IRA for a person who has no funds in any Trad IRA, SEP IRA, SIMPLE IRA, or rollover IRA. Because it is Post Tax, it is Basis. They should not invest it until it transfers to the Roth IRA. And the tax form issued for the money out, 1099-R, might not have the right code for the conditions for this taxpayer. Their Basis needs to be entered so that it reflects a nontaxable conversion.

A Backdoor is just a conversion. The magic is the Basis factor.