What does IMPT mean or stand for?

Check with your employer. Box 14 is a "catch all" box. The IRS allows employers to enter into Box 14 anything of importance that is not reported in any other box. The amount may be taxable, deductible or just there for informational purposes.

Most likely TurboTax is asking for a code so it knows what to do with this number. You can use Other (not classified) if nothing else fits.

It might mean Imputed Income.  If so, though, it it usually recorded on Form W-2 in Box 12.  But, as suggested, check with your employer.