Final answer:
The symbol Ca on the periodic table stands for calcium, an element with the atomic number 20, and it should not be confused with other one or two-letter element symbols.
Step-by-step explanation:
The symbol Ca on the periodic table represents the element calcium. This symbol is derived from the first and second letters of its English name, with only the first letter capitalized to distinguish it from other notations, as observed with other elements (for example, 'Co' represents the element cobalt, whereas 'CO' is the compound carbon monoxide).
It is important to note that the symbols for elements on the periodic table are unique to each element. For instance, 'C' represents carbon, 'Co' symbolizes cobalt, 'Cl' is the symbol for chlorine, and 'Ca' is specifically for calcium, as indicated by the periodic table in figures provided in chemistry textbooks.