It can depend on the application you are using.
For example, in AutoCAD (a computer aided drawing package) these are referred to as 'X-Refs' (external references). You can have as many references as you like, inserted as many times as you like. When one of the references is updated, it automatically updates all the others in the file (you would typically have a 'template file' with x-ref's inside it).
In Microsoft Word, 'Headers and Footers' repeat information which need only be updated in one place and is reflected throughout the file. To repeat 'content' or 'data' you could use 'Content Controls'. Here is an article covering many of the options: https://gregmaxey.com/word_tip_pages/repeating_data.html
However, I feel this is getting off the topic of your original question.
Personally, I would use 'Boiler Plate' to describe file templates or repeated data/fields inside the files: