Yes. Portability must be elected on a timely-filed federal estate tax return. This is the case even though a federal estate tax return would not otherwise be required, such as if the estate of the deceased spouse is below the threshold for federal estate taxation.
Portability is where the surviving spouse can use the amount of federal estate tax exclusion that their deceased spouse left unused at their death. Portability has been part of the law since 2011, though it was temporary until 2013.
A state estate tax is a tax levied by a state government upon the estate of a deceased person. It is levied in much the same way as the federal estate tax. A state inheritance tax is a tax levied by a state government that varies depending upon the relationship of the inheritor to the deceased person. Many states have a separate state estate or inheritance tax which kicks in at a lower level than that of the federal government.