Where are you trying to mail merge from? The territory is on the opportunity and I know you can merge from the opp and bring over the territory, you just go to your mail merge template and do the following;
1. Insert Field
2. Type MM and it will bring you to Mail Merge
3. Under Field Name: Copy and Paste the Territory Name Field from Territory Management or from directly from the Opportunity Fields
It will only merge from certain locations such as the Opportunity itself, unless you use a tool like Conga Merge or you use a Cross Object Formula to bring in the territory name from which you want to merge.
Where are you trying to mail merge from? The territory is on the opportunity and I know you can merge from the opp and bring over the territory, you just go to your mail merge template and do the following;
1. Insert Field
2. Type MM and it will bring you to Mail Merge
3. Under Field Name: Copy and Paste the Territory Name Field from Territory Management or from directly from the Opportunity Fields
It will only merge from certain locations such as the Opportunity itself, unless you use a tool like Conga Merge or you use a Cross Object Formula to bring in the territory name from which you want to merge.
Let me know if that helps.