It is binary code used by electronic equipment to handle text using the English alphabet, numbers, and other common ascii character table pdf. ASCII is an abbreviation for American Standard Code for Information Interchange. ASCII was developed in the 1960s and was based on earlier codes used by telegraph systems.
The code includes definitions for 128 characters: most of these are the printable characters of the alphabet such as abc, ABC, 123, and ? There are also control characters that cannot be printed but instead control how text is processed, to start a new line for example. Those are in the left column in the table below. Most of the control characters are no longer used for their original purpose.
Sometimes someone talks about a file or document in ASCII, meaning it is in plain text. Seven bits allowed a parity bit to be included in each byte sent over a serial port or modems, this bit is used for avoiding errors.
This was more important years ago when connections were often noisy. It was only meant for English and doesn’t work well for most other languages.