What this means is that Instagram can now effectively sell the use of your username, profile picture, photos you've taken and records of what you've liked or commented on to another company — like an advertiser — and they don't have to pay you in order to do so. And you can't stop them.

Facebook's terms in this regard are similar, but Facebook does explicitly grant you the ability to adjust how your name and profile photo are used for ads and commercial content:

You can use your privacy settings to limit how your name and profile picture may be associated with commercial, sponsored, or related content (such as a brand you like) served or enhanced by us. You give us permission to use your name and profile picture in connection with that content, subject to the limits you place.