
Hi @Maarten Van Elsen ,
1.Open the Term Store management tool
Site settings > Site Administration > Term store management > Return to classis
2.Click "View a sample import file" to download a copy of the import file.
Term Store Management Tool > GENERAL > Sample Import > View a sample import file
3.Open the sample CSV file, populate the file as per your requirement. Then import the file into the desired group to create a new term set.
Right click Group > Import Term Set > Choose file > select your CSV file
For Reference: Import term sets
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