What’s the definition of a tag, as it pertains to digital advertising?

What’s the definition of a tag, as it pertains to digital advertising?

 

• A tag is a large snippet of code that’s placed on the conversion page of a website.
• A tag is a small snippet of code that’s placed on the conversion page of a website.
• A tag is a large snippet of code that’s placed on the home page of a website.
• A tag is a small snippet of code that’s placed on every page of a website.