To prevent your Shopping ads from appearing for certain search terms, you would:
add negative keywords to your campaign or ad group
remove the related search terms from your product titles in your product data
remove products from your product data
put shorter descriptions in your product data
While Shopping campaigns don’t use keywords to target your ads, you can use negative keywords to help prevent your Shopping ads from appearing when you don’t want them to.
Read more here: https://support.google.com/adwords/answer/6275313