A telemour, for those of you not familiar with the term, is a partner of your metamour who is not the shared one between you. (If you're dating Bob, who is married to Carol, and Carol dates Denise and Eric, Denise and Eric are your telemours.) The term was popularized by Page from Poly.Land and I like it, it fits the add-a-prefix pattern of metamour, tele being Greek works, and it means far away so you can use it even for those folks in your polycule you feel only the most distant awareness of.
"But Laura," you might ask, "why would I need a word for folks in my polycule I have only a distant awareness of?" Or, "I already have a name for these people, I call them my meta-squareds, girlfriends twice removed, metas-in-law, friends if I'm friends with them or polycule members if I'm not, who needs a standard word?" and if your term works for you and your polycule members, keep using it! But shorthand is convenient, humans like labels, and just like metamours, this is a unique polyamorous relationship. A monogamous person isn't going to meet their boyfriend's girlfriend's girlfriend - or ever tell a story about them where their connection might matter. Just like you can of course choose not to use any particular jargon and instead use descriptive sentences for relationships, behavior, or interactions, you can avoid this one - but it might be handy.
That's really the choice with labels - do you want shorthand? Do you want to have a nod that an in-group will get and understand, even if you have to explain to an out-group? Then a label is the right choice. Once you've used the label, on a 1-1 level it's better to clarify that you both interpret the label the same way - do you both mean friendly but not best friends or spending all your time together when you say you're "Kitchen Table" with metamours, or does one of you hear "garden party" out of that combination of activities and mean let's spend tons of time together and be invested in each others' major life decisions as much as possible when Kitchen Table is the label? Shorthand and labels are great for moving quickly and clarification important for working 1-1.
Telemour as a word is great for "how do you know her?" "She's my telemour - X's partner." "Oh, ok," but sometimes requires more explanation if the person you're talking to doesn't already know your metamour, and if you have an independent relationship, just explaining that can be more useful "My friend Denise," not "my telemour Denise- Carol's partner". Pick and choose the word you need when you need it. Sometimes this is the right one for the people in your constellation further out than metamours and sometimes it isn't.