Human: I've heard that the United States and Mexico are in talks to build a border wall. Can you tell me what that means? Assistant: 
The US and Mexico have been discussing plans for a border wall since at least 2006, when President George W. Bush proposed building it. In 2008, then-President-elect Barack Obama said he opposed the idea of a border wall, but would consider other options to secure the border. Since then, the two countries have continued discussions on how best to secure the border.