When a person performs `Umrah during the months of Hajj and then performs Hajj in the same year, thus enjoying the state of removing the ritual consecration in between, this is called Tamattu`. But the point here is that one should assume ihram for `Umrah during the months of Hajj, not before them.
The Standing Committee for Islamic Research and Ifta‘ (i.e., issuing edict), stated,
First, if a person assumes ihram for `Umrah at the end of Ramadan; performs Tawaf and Sa`i only on the first night of Shawwal; performs Tahallul (removal of the state of ihram) after finishing the `Umrah; and afterward performs Hajj in the same year, this is not considered Tamattu` because this person’s ihram for `Umrah was not assumed during the months of Hajj.
Second, as for the person who assumes ihram for `Umrah after going beyond the Miqat and then performs `Umrah and travels to Madinah and then assumes ihram at the Miqat for another `Umrah and performs it, the second `Umrah does not cancel the first required damm (i.e., animal sacrifice for rectification of error or mistake committed during hajj or Umrah) he or she had to offer to expiate assuming iharm after the Miqat for the first `Umrah.