What do you mean by delta as a symbol in physics?
Delta is a symbol that denotes a change in something. In physics the delta-v is used to calculate the change in velocity, or change in velocity over time.
That pyramid symbol (or better defined as a triangle as to not get confused with lower mathematics / geometry) simply means a change in something. The actual term is "delta" and it is also known as the derivative of y as seen here: (delta) y / (delta) x. (delta) y / (delta) x would be read as the change in y with respect to x.
In physics, the lambda symbol, which is the Greek letter λ, represents the wavelength of any wave. The wavelength of a wave is the distance over which the curvature of a wave's shape repeats itself. Types of wavelengths often applied with this symbol include light waves, water waves, and sound waves.
Select Insert | Symbol, scroll down to Mathematical Operators subset, highlight the delta (∆) symbol, and click Insert. For a mac, if you're in Microsoft word, just hit Option+J and that should produce the ∆ symbol . If you prefer the lower case delta, just scroll through the list until you find the symbol you want.
There are many meanings. The most common one is "change in". So delta x is the change in x. This form is often used in calculus where it means very small changes in x. But there is also the Dirac delta function, a fundamental mathematical underpinning for quantum physics. A delta can also be a quadrilateral which is otherwise known as an arrowhead.