A character in UTF8 can be from 1 to 4 bytes long. UTF-8 can represent any character in the Unicode standard. UTF-8 is backwards compatible with ASCII. UTF-8 is the preferred encoding for e-mail and web pages.
Because the character sets in ISO-8859 were limited in size, and not compatible in multilingual environments, the Unicode Consortium developed the Unicode Standard. The Unicode Standard covers (almost) all the characters, punctuations, and symbols in the world. Unicode enables processing, storage, and transport of text independent of platform and language. The default character encoding in HTML-5 is UTF-8. If an HTML5 web page uses a different character set than UTF-8, it should be specified in the meta tag like: <meta charset="ISO-8859-1">
Unicode is a character set. UTF-8 is encoding.
Unicode is a list of characters with unique decimal numbers (code points). A = 65, B = 66, C = 67, ....
This list of decimal numbers represent the string "hello": 104 101 108 108 111
Encoding is how these numbers are translated into binary numbers to be stored in a computer: UTF-8 encoding will store "hello" like this (binary): 01101000 01100101 01101100 01101100 01101111