With draft talk starting up in earnest, we will be hearing terms like this. This website does an excellent job of explaining exactly what they mean.
http://insidethepylon.com/football-101/glossary-football-101/2015/10/06/itp-glossary-hip-fluidity/
http://insidethepylon.com/football-101/glossary-football-101/2015/10/06/itp-glossary-hip-fluidity/