"Indirect descendants" is a term that I believe is rarely used in the US.
"Indirect Descendants" are those found in collateral lines as opposed to
"direct descendants" found in one's direct line. These collaterals
include aunts, uncles, nephews nieces, cousins, XcousinsYtimes removed,
e.g. 1C2R, great aunts, gg uncles,etc. Collateral line relatives are
found in *compiled genealogies. Direct line relatives are found in
*pedigree and Ahnentafel charts*.
John H. Wray, PhD, CG, Tucson, AZ