Traditional IRA is tax deductible and tax deferred for any capital gain. Similar to 401K.
The difference is in Traditional IRA account you have access to the whole market of stock, ETF and mutual funds, while 401K plan usually only provide a limited choice. Even when Traditional IRA and 401K are managed by the same invesmtment company, the choice of investment is much much more in Traditional IRA.
But, sometimes more choice might not be a good thing. You have more choices to fail as well.
But if the IRA you talking about is Roth IRA, the rule is different.