Often you will hear me say before a deadlift or a squat or a press, "stay tight." This is a cue to go from being slack to rigid, particularly to maintain midline stabilization. At CrossFit Invictus, they refer to this practice as 'bracing,' and they have a nifty little flowchart that outlines midline stabilization. Take a look.
The following is from CrossFit Invictus, which in turn is drawing on the super knowledgeable Kelly Starr.