What is it called when you put several initials together to make a word?

There's not a single specific term for putting initials together to make a word. However, here are some options depending on the context:

Formal:

* Acronym: This is the most common term for a word formed from the first letters of a phrase. It usually applies to words that are pronounced as a single word, like "NATO" (North Atlantic Treaty Organization).

* Initialism: This term is used when the letters are pronounced individually, like "FBI" (Federal Bureau of Investigation).

* Abbreviation: A broader term that encompasses acronyms and initialisms, as well as other shortened forms of words or phrases.

Informal:

* Wordplay: This refers to the playful use of language, and putting initials together to form a word can be a form of this.

* Shorthand: This describes a shortened way of writing or expressing something, and initials can be a form of shorthand.

The best term to use depends on the specific situation and the type of word being formed.