IRA conversion means: convert from your traditional IRA money to your ROTH IRA account. You can do this any time, for any amount. There might be tax involved. But IRA conversion is a legal concept, not a financial trick.
Backdoor ROTH IRA contribution: this is a legal/financial trick. It involved two steps: (1) contribute to your tradtional IRA (up to an annual limit); (2) convert your tradtional IRA contribution in (1) into your ROTH IRA account, using the legal concept of IRA conversion. Because it involves (1) contribute to your tradtional IRA, the "backdoor ROTH IRA contribution" has deadline and amount limit.
Some of the "backdoor IRA" people are talking about on this forum is merely just IRA conversion.
