What does Overall Length, Depth and Height mean?

Overall Length, Depth and Height refers to overall dimensions of your furniture,  which needs to include anything that sticks out, and measured at the widest parts.  For an item such as a BBQ, overall length would include any curved handles at the sides, and overall depth would also include the knobs/handle at the front which often sticks out. 

The Broom Handle Technique refers to a method which can help you in measuring awkward overall dimensions, and you don't have to use a broom handle, it just needs to be straight and solid. 

For example- measuring the overall Depth of the Bench/Sofa (that tilts back) –

I would hold the broom upside down (only interested in the long straight broom handle) pressed up against the back of my Bench/Sofa positioned perpendicular to the ground (straight up, and not at an angle at all).  This now allows me to stand closer to the front of my Sofa/Bench, extend my tape measure to touch the broom handle thus allowing me to accurately read the measurement shown from the very back of the sofa to the very front.