IRA CDs are really just CDs that financial institutions have labeled as such and that they may try to make more attractive with this label and by offering higher rates. They have the same characteristics as other CDs: you agree to let the financial institution use your money for a set period of time in return for a fixed rate. Early withdrawal penalties apply. Moreover, it is important to note, that taking your money out of an IRA as part of your withdrawal can trigger penalties related to your retirement account.
You may also invest IRA funds in a CD that is not labeled an IRA CD. You should therefore check the best CD rates here. With a traditional IRA, your contribution to the account is tax deductible, lowering your taxable income. If you have a Roth IRA, you will not receive a tax deduction for your contribution, but your earnings in the IRA will be tax deferred, as long as you refrain from withdrawals from the IRA until permitted. Most IRAs CDs are fixed-rate CDs. However, some banks offer variable-rate CDs.
More information can be found in BestCashCow's Fixed Rate IRA CD Guide.