It is probably asking if your husband made after-tax contributions to the pension plan while he was working. If so, the total of these after-tax contributions forms the "cost" or "basis" of the pension. When the pension is paid out to you over time, then that part which is a return of basis (there is a formula for that) is not taxable - because you already paid tax on the amount already.
It is possible to make such after-tax contributions to a pension plan, but not necessarily likely. If you go back to last year's return and see that the entire amount received from the pension in 2016 (i.e., the amount on the 1099) was taxable, then your basis is probably zero - so just enter that.
