Hexadecimal A is a numerical system that uses base 16, meaning it uses the numbers 0-9 and the letters A-F to represent values. It is commonly used in computing and digital electronics as a way to represent binary data. The term hexadecimal is derived from the Greek words for six and TEN, as it is a base 16 system. The crossword solution for the term hexadecimal A is TEN, which is the number 10 in the decimal system.