What is it called when your boss takes out money for an IRA but keeps it instead?

Generally it is called stealing.  Specifically, it depends on how much has been taken.  It may fit under the definition of embezzlement under your state laws.  It probably violates a whole host of banking laws as well as criminal laws. You need to speak with an attorney in your area on the matter as soon as you possibly can.  Please make sure that you have the necessary proof regarding the deductions (paycheck stubs or written breakdowns from the employer showing the deduction weekly or however it was taken out) and any correspondence or paperwork that your employer had you fill out to open the IRA, take out money, etc.   Good luck to you. 

If you have an agreement with your employer per written instructions where a portion of your pay checks are to be placed in you own individual retirement account (IRA) by your employer and they are not where the withheld portion by the employer is used for his or her own use, that is called "theft", "breach of a fiduciary duty" and just plain "wrong".

If this is what is happening to you, go down to the nearest labor department office in your community with documentation of what is supposedly happening by your employer with respect to a portion of your pay checks that is supposed to be allocated to your IRA and deposited by your employer to make a complaint about the situation.

You need to know that is some cases there are periods when the employee's contribution into the any retirement plan through a business can be deposited by an employer if the retirement plan is not an IRA, but is a 401 k retirement plan.

Good luck.