What is a lightbox ad?
A type of ad format that shows extra information (“extending” from your text ads) about your business
A mobile text ad
A cross-screen expandable ad format that optimizes for taps/swipes on mobile and mouse-overs/clicks on desktops
A remarketing specific ad format to announce new features of your app
Read more here: https://support.google.com/partners/answer/6135143?hl=en