An acronym is a word formed from the initial letters of a phrase, with each letter representing the first letter of a word in that phrase.
GUI is an example of an acronym. It stands for Graphical User Interface. By taking the first letters of each word G, U, and I, you get the acronym GUI.
An initialism is formed from the initial letters of a phrase, with each letter representing the first letter of a word in that phrase.
For example, HTML is an initialism; it stands for HyperText Markup Language and is pronounced by spelling out each letter H, T, M, L.
Both acronyms and initialisms are types of abbreviations. The distinction is acronyms are pronounced as words and initialisms are pronounced as individual letters.
Maybe replace the Graphical User Interface with something else.
Then add it back in as an example of both.
Here is a suggested change:
An acronym or initialism is formed from the initial letters of a phrase, with each letter representing the first letter of a word in that phrase.
* GUI is an example of an acronym. It stands for Graphical User Interface. By taking the first letters of each word G, U, and I, you get the acronym GUI.
* HTML is an initialism; it stands for HyperText Markup Language and is pronounced by spelling out each letter H, T, M, L.
Both acronyms and initialisms are types of abbreviations. The distinction is acronyms are pronounced as words and initialisms are pronounced as individual letters.