This option is available on Matching Column (Step 2) of Update, Add & Export feed only. 
The template suffix field allows updating the product to return the custom name of an alternate template. Returns nil if an alternate template is not being used.
For example,
If your feed file doesn't have any column as a template suffix and you want to apply it as a Template for all your products. You can select the option as Static and enter the value Template in the field.
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