they are small suggestive animations that inform the user of current processes taking place. they serve to inform the user and add life to a product. can inform of current system status too, on or off.
progressive enhancement
they are small contained product moments that accomplish a single task such as providing feedback and guiding users. they are often subtle and informative.
the best interface is no interface. book.
a light animation when a user likes a post to indicate the action was successful.
a progress bar that fills as a file uploads.
the sound of refresh when a user pulls down to update a feed.
the ability to see the other person is typing in a text chain.