In addition to analysing your chromosomes 1 to 22, the Family Finder test also analyses your X chromosome, though it appears in the expanded view of your match list and also on the chromosome browser, I have found very little explanation about this on the Family Tree DNA site.

X-DNA is useful when trying to work out how you may connect to your matches, mainly because of its very distinctive inheritance pattern.

You can download circular charts showing which of your ancestors have passed on X-DNA to you on The Genetic Genealogist website - along with a good explanation about how it works, and on this page of  Debs Delvings you can download Word documents where you can enter the names of your own ancestors who have passed on X-DNA to you,  but briefly ...

Every female child inherits TWO X-chromosomes - one from each parent.  These combine and a single X chromosome, containing segments in varying proportions from both her parents, is passed on to  her children - both male and female.

Every male child inherits an X and a Y chromosome - the Y from his father and the X from his mother.  However, he only passes on the X chromosome (unchanged) to his daughters.

As a result, females inherit X-DNA from more of their ancestors than do males.

However, I have noted small amounts of shared X-DNA even between project members whose shared ancestry is known, but where there should not be any shared X-DNA according to the inheritance pattern.  This is probably just evidence of DNA segments which are Identical by State (IBS) rather than Identical by Descent (IBD), but could indicate that in some instances there may be shared ancestry on more than one branch!

Something that needs a lot more exploration!!