An atomic symbol is the 1-3 letter abbreviation of a chemical element. Examples include:
- Hydrogen (H)
- Iron (Fe)
- Ununquadium (Uuq)
All naturally occurring elements (Atomic numbers 1-92) and named man-made elements (93-112) have either 1 or 2 letter abbreviations. The 3 letter ones are always unnamed man-made elements (113-118). These three letter abbreviations are temporary IUPAC names that are made from the roots of Latin and Greek numbers. Take for instance Ununquadium, atomic number 114. The root un means 1 and quad means 4. Since you have two un roots and a quad root you get 114 (ununquad). Couple that with the regular -ium ending for most elements that form positive ions and you get the temporary name.