Annulus
The annulus is the space between two tubular. In drilling, unless specified, it is considered as the space between the drilling string and the open hole or casing. Common abbreviations used in the drilling industry are TCA (Tubing Casing Annulus) and CCA (Casing to Casing Annulus).
Azimuth
Azimuth defines the direction of the well. It is measured in a horizontal plane and is expressed as the angle from a reference plane, usually 'True North'. The horizontal plane is divided into four quadrants of 90 degrees each with the reference plane as zero. If the azimuth at a survey point is 225o, it means that the well at that point is in the 3rd quadrant and is heading in South West direction in reference to 'True North'.
Adjustable Kick Off Sub
AKO (Adjustable Kick Off) sub or Bent Sub is a small segment of the drill string which is tilted at an angle rather than being straight. It is run above the bit and below the power section in the drill string and is used for drilling directional well or for kicking off from a vertical well. Running the AKO sub in the string makes it possible to steer the well as needed through sliding. The tilt of the sub depends on tool size, hole size, and DLS (Dog Leg Severity) requirement.