401(k) = retirement account, usually matching benefits from an employer, etc. Credit union = banking facility, eg, checking and savings accounts, etc.
A 401K is a retirement plan.....once you put money into it, it usually put into the stock market where it has a chance to grow (or lose, in the latest enviroment)....Money put into a credit union is a savings account...where it is safe, but interest on your money right now is running about 2%. If you ever want to get your money out of a 401K, you have to pay taxes and penality, until you turn 59 1/2.
One thing about a 401K, is that it is deducted from your taxable gross pay...so you pay less taxes out of your check. That's not true for putting it into the credit union.
pWhat exactly is a 401(k)?