Acronyms: These are words formed from the first letters of a phrase. For example, "NASA" stands for "National Aeronautics and Space Administration".
Initialisms: Similar to acronyms, but the letters are pronounced individually, like "FBI" for "Federal Bureau of Investigation".
Blend words: These are words formed by combining parts of two or more words. For example, "smog" comes from "smoke" and "fog".
Portmanteaus: This is a specific type of blend word, often used in informal contexts. For example, "brunch" is a blend of "breakfast" and "lunch".
Abbreviations: These are shortened forms of words or phrases, often using periods. For example, "etc." is an abbreviation of "et cetera".
The best term to use depends on the specific context and the way the shorter word is formed.