Delta facts for kids
Greek alphabet  

Αα  Alpha  Νν  Nu 
Ββ  Beta  Ξξ  Xi 
Γγ  Gamma  Οο  Omicron 
Δδ  Delta  Ππ  Pi 
Εε  Epsilon  Ρρ  Rho 
Ζζ  Zeta  Σσς  Sigma 
Ηη  Eta  Ττ  Tau 
Θθ  Theta  Υυ  Upsilon 
Ιι  Iota  Φφ  Phi 
Κκ  Kappa  Χχ  Chi 
Λλ  Lambda  Ψψ  Psi 
Μμ  Mu  Ωω  Omega 
Other letters  
Ϝϝ  Digamma  Ⱶⱶ  Heta 
Ϻϻ  San  Ϙϙ  Koppa 
Ϡϡ  Sampi  Ϛϛ  Stigma 
Ϸϸ  Sho  

Delta (uppercase/lowercase Δ δ), is a letter of the Greek alphabet, used to represent the "d" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 4. Letters that came from it include the Roman D and Cyrillic Д.
In mathematics, the uppercase letter Δ can be used as symbol to represent "change" in a variable (e.g., ). It can also be used to represent discriminant—a key algebraic expression used to determine the number of roots a polynomial has. The lowercase letter , on the other hand, is often used to denote small quantities in proofs involving limit, a key concept on calculus is based on.
In molecular chemistry, the lower case Greek letter δ is used to represent a partial charge. This is always less than the unit charge associated with an ion, but has no real fixed value.
A river delta is so named because its shape approximates the uppercase letter delta.