Definitions for "Focus Lock"
Pressing the shutter button halfway on an automatic camera locks the focus on the subject in the centre of the viewfinder. To photograph a subject that is off to one side, centre the subject, press the shutter release button halfway, shift the subject back to the desired position, then press the shutter release button all the way.
Pre-focusing the camera and then moving it to re-compose the image before capturing it. Accomplished by half-pressing the shutter button and keeping it held at that position while moving the camera to another point before pressing it all the way to capture the image
Used to focus on subjects that are off-center. Center the subject in the viewfinder, press the shutter button halfway down, recompose the picture while you continue to hold the button, then press the shutter button all the way down to take the picture.