Split
Split turns up in 2 fields: refractories, HVAC. Here is what it means to the people in each one.
Split in refractories
Brick of standard length and width but reduced thickness, used to adjust course heights.
A brick of standard 9 x 4.5 inch face but thinner than a straight, commonly 1.25 inches and also 1, 1.5 and 2 inches. Splits let bricklayers bring courses to the right height, finish against steelwork and close up sections without cutting. Ordering splits rather than sawing straights in the field saves blades and keeps dimensions true, especially with dense high-alumina brick.
"Gap under the shelf angle is an inch and a quarter, lay a row of splits instead of cutting straights."
Split in HVAC
The temperature difference between return and supply air across a coil, used as a quick health check.
On a typical cooling system, techs expect a split around 16 to 22 degrees F, lower in humid weather because more of the coil's work goes into removing moisture. A low split suggests low charge or too much airflow; a high split suggests low airflow. Techs also talk of condenser split, the gap between condensing temperature and outdoor air. Split is a starting clue, not a charging method.
"Split's only 9 degrees, return 78 and supply 69, put gauges on it and check the airflow too."