Quick answer
Two names combined into one word are most often called a portmanteau — the formal linguistic term. Informally, the same result is called a mashup name, a couple name combination, or, for a romantic pairing, a ship name. All four describe the same thing; they differ by context and tone, not by method.
Search for this and you'll see all four terms used almost interchangeably. That's accurate. But it helps to know exactly where each one comes from, and when people actually reach for it.
Portmanteau
Portmanteau is the correct linguistic term for a word built by blending the sound and meaning of two others. Letters get dropped or overlapped at the seam. The word itself comes from a French term for a two-part travel case. Lewis Carroll first used it this way, in Through the Looking-Glass. Everyday English is full of portmanteaus: brunch (breakfast + lunch), smog (smoke + fog), motel (motor + hotel). A blended couple name is just a portmanteau built from two people's names instead of two nouns.
Ship name
Ship name is the fandom term for the same idea, used for a romantic pairing. "Ship" is short for "relationship." The term started in fan communities, blending the names of two characters or celebrities fans wanted to see together — think Brangelina, or Bennifer. Couples have since adopted the word for their own blended name, even outside fandom. Every ship name is a portmanteau. But not every portmanteau is a ship name, since the term only applies to romantic pairs.
Mashup name
Mashup name is the casual, everyday version of the same idea. You'll hear it most in conversation and on social media, where "portmanteau" can sound too formal. If someone asks "what's your mashup name?" they mean the same thing as a portmanteau or ship name. It's about tone, not method.
Couple name combination
Couple name combination is the plain, descriptive phrase most people actually type into a search bar. It's the most neutral of the four — it doesn't lean romantic, fan-culture, or casual. It's also the most literal: two partners' names, combined. This is the term CoupleNaming's tool is built around.
Portmanteau vs. Compound Word
These two get confused often, but they're built differently. A compound word joins two complete words with nothing removed — bedroom, sunflower, toothbrush. A portmanteau blends only parts of each word, trimming or overlapping at the seam — brunch, not "breakfastlunch." Name blending works the portmanteau way by definition: Jordan + Alexis becomes Jordexis, not "JordanAlexis."
Two More You'll Hear: Combinator and Masher
Two informal terms round out the list. Combinator usually refers to the tool itself — the app or generator that produces the blend — rather than the resulting name. Masher (or "name mashup") is a casual synonym for mashup name, used the same way in everyday conversation. Neither is a formal linguistic term, but both show up often enough in search and casual speech to be worth knowing.