Final answer:
The expression [a-zA-Z] is a regular expression pattern that matches any single character from the English alphabet, both uppercase and lowercase. It is commonly used in regular expressions to match alphabetic characters.
Step-by-step explanation:
The expression [a-zA-Z] is a regular expression pattern that matches any single character from the English alphabet, both uppercase and lowercase. The [a-zA-Z] pattern matches a single character between a and z (inclusive) or between A and Z (inclusive).
For example, if you apply the pattern [a-zA-Z] to the string 'cAT12', it will match the 'c', 'A', and 'T' characters, ignoring the digits '1' and '2'. This pattern is commonly used in regular expressions to match alphabetic character.