Android 6.0 Marshmallow’s text selection behavior changed, pushing the toolbar from the top of the screen to a floating one that pops up right above your finger. It also made this popup expandable and accessible to developers, some of which have since updated their apps to take advantage of this new option. First, Google Translate added a system-wide Translate button, making it possible for users to convert any word or sentence they come across into another language.
Wikipedia Beta Adds System-Wide Search From Floating Text Selection Popups In Marshmallow was written by the awesome team at Android Police.
Source: Andriod Police