Character Set- A defined list of characters recognized by the computer hardware and software. Each character is represented by a number. The ASCII character set, for example, uses the numbers 0 through 127 to represent all English characters as well as special control characters. European ISO character sets are similar to ASCII, but they contain additional characters for European languages.

ASCII-Acronym for the American Standard Code for Information Interchange. Pronounced ask-ee, ASCII is a code for representing English characters as numbers, with each letter assigned a number from 0 to 127. For example, the ASCII code for uppercase M is 77. The basic ASCII set uses 7 bits for each character, giving it a total of 128 unique symbols.
ASCII file-A text file in which each byte represents one character according to the ASCII code. Contrast with a binary file, in which there is no one-to-one mapping between bytes and characters. Files that have been formatted with a word processor must be stored and transmitted as binary files to preserve the formatting. ASCII files are sometimes called plain text files.Extended ASCII-The extended ASCII character set uses 8 bits, which gives it an additional 128 characters. The extra characters represent characters from foreign languages and special symbols for drawing pictures.

ANSI- Acronym for the American National Standards Institute. Founded in 1918, ANSI is a voluntary organization composed of over 1,300 members (including all the large computer companies) that creates standards for the computer industry. For example, ANSI C is a version of the C language that has been approved by the ANSI committee. To a large degree, all ANSI C compilers, regardless of which company produces them, should behave similarly.
In addition to programming languages, ANSI sets standards for a wide range of technical areas, from electrical specifications to communications protocols. For example, FDDI, the main set of protocols for sending data over fiber optic cables, is an ANSI standard.

Unicode- A standard for representing characters as integers. Unlike ASCII, which uses 7 bits for each character, Unicode uses 16 bits, which means that it can represent more than 65,000 unique characters. This is a bit of overkill for English and Western-European languages, but it is necessary for some other languages, such as Greek, Chinese and Japanese. Many analysts believe that as the software industry becomes increasingly global, Unicode will eventually supplant ASCII as the standard character coding format. 

Decimal- Refers to numbers in base 10 (the numbers we use in everyday life). For example, the following are decimal numbers:
9,100345000 and -256.
Note that a decimal number is not necessarily a number with a decimal point in it. Numbers with decimal points (that is, numbers with a fractional part) are called fixed-point or floating-point numbers.
In addition to the decimal format, computer data is often represented in binary, octal, and hexadecimal formats.

Hexadecimal- Refers to the base-16 number system, which consists of 16 unique symbols: the numbers 0 to 9 and the letters A to F. For example, the decimal number 15 is represented as F in the hexadecimal numbering system. The hexadecimal system is useful because it can represent every byte (8 bits) as two consecutive hexadecimal digits. It is easier for humans to read hexadecimal numbers than binary numbers.
To convert a value from hexadecimal to binary, you merely translate each hexadecimal digit into its 4-bit binary equivalent. Hexadecimal numbers have either an 0x prefix or an hsuffix. For example, the hexadecimal number
0x3F7A




 https://www.microsoft.com/typography/unicode/cs.htm