initialism

An initialism is an abbreviation formed from the initial letters of the words in a phrase, and it is typically pronounced letter by letter rather than as a single word. It is a distinct category from an acronym, which is usually spoken as a word.

Common examples include FBI, CIA, IBM, and USB. These strings are usually written in uppercase and are not pronounced as syllables. In older style usage, periods were sometimes included (U.S.A., U.N.), but modern practice often omits them. Initialisms are widespread in government, business, science, technology, and everyday language.

Initialisms differ from acronyms in pronunciation, but both are formed from the initial components of longer terms. If a term is widely spoken as a word, such as NASA or radar, it may function more like an acronym or a backronym rather than a strict initialism. Some initialisms eventually become lexicalized and are treated as units in writing and speech.

Stylistic conventions for initialisms vary by language and style guide. In English, capitalization is common, and periods are optional depending on the house style. In technical writing, initialisms are often defined on first use, with the full phrase followed by the initialism in parentheses, and then used alone thereafter.

The use of initialisms expands with new technologies and institutions, resulting in continual updates to lexicons and documentation. They enable concise reference to complex terms but can pose readability challenges for unfamiliar readers.