What does delta △ mean?

The symbol delta △, which is an upward-pointing triangle, means change, difference, or variation in most scientific and mathematical contexts. The uppercase Greek letter delta Δ, often shown as △ in simple text, is universally used to denote change calculated as final value minus initial value. For example, △T means change in temperature, △t means change in time, and △x means change in position. If △ is positive, something increased. If negative, it decreased. In chemistry, △ written before a reaction means heat is applied, indicating that the reaction requires heating to proceed. For example, △ above an arrow means heat. In physics, △ can mean discriminant or change in energy. In geography, the same triangular shape represents a river delta, a landform at the mouth of a river. In mathematics, △ can also mean a triangle as a shape, as in △ABC means triangle ABC. In set theory, △ can mean symmetric difference. In everyday language, people use △ as a shorthand for difference or improvement, such as what's the △ between these two plans. The symbol is powerful because a triangle is the strongest shape and visually conveys stability and upward movement. So when you see △, think change, difference, heat, or triangle, with change being the most common meaning in STEM fields.