In genealogy, the phrase “direct descendant” is used regularly. Isn’t that redundant? Either you are a descendant of a particular person or you’re not.
Some genealogy reference books attempt to define indirect descendant as “descended from a common ancestor but through different lines” which, in my opinion, means you are potentially distant cousins, but you are still each (direct) descendants of a common ancestor.
You’re an indirect descendant of Ben Franklin if you’re a direct descendant of his sister.
It’s an imprecise term, and I avoid it in my genealogical discussions, but lots of others employ it.
If I’m a descendant of Ben Franklin’s sister, I am a descedant of their father, but am I not a decesdant of Ben, at least not in a biological sense.
Sounds like “indirect descendant” is way for some people to try to claim a relationship that doesn’t exist - e.g. I’m an (indirect) descendant of George Washington.
Oh, the relationship exists, all right. It’s one of collateral relations. And kingships have turned on such things. How do you think the German-speaking George I ended up King of England?
I also posit that “indirect descendant” sounds better to a lot of people than claiming Ben Franklin as a “cousin”. He would be one, something like first cousin 7 times removed.
Personally, I’d opt for cousin. Heck, Prince William of England is 27th cousin, 9 times removed.
George W Bush is an indirest descendant of Franklin Pierce the 14th President of the United States through his mother Barbra Pierce (Bush).
Ah, but George I got the nod because he was a direct descendant of the Electress Sophia (his mum), who in turn was a direct descendant of James I & VI (her grandfather).
Consider the following three sentences:
A. I am a descendant of George Washington.
B. I am a direct descendant of George Washington.
C. I am an indirect descendant of George Washington.
B = A, therefore “direct” is redundant and can be left out.
For C, if George is a great-great-…-parent, then it is the same as A.
If I am related to George through a sister, cousin, brother, etc., then I am not his descendant, but we are, of course, relations.
What’s wrong with just being cousins or a grand-grand-…-nephew? Why the rush to claim descendancy from someone who isn’t your ancestor?
Of course, since George Washington had no children, no one is his direct descendant… 
Zev Steinhardt
No. No one is his descendant. 
While I agree with you, we are now faced with semantics. Some people recognize indirect descent to mean what was described. I know what they’re talking about when the term is used, even if I think it’s silly. But so far they’ve refused to change for my benefit.
I agree. Since my OP asked what an “indirect descendant” is, I think you have answered the question.
Direct Descendant: a biological descendant of a person.
Indirect Descendant: a blood relation, but not a biological descendant of a person. Used by some people because it sounds better than “third cousin, twice removed” or similar relationships.
Thanks everyone. 
Well, then we’ll just have to agree to… um, agree, I guess.