What is the 'ancestral term' in the LS coupling scheme?
"Ancestral Terms" are terms such as parent and grandparent terms that couple to form the final term.

For example, if you see $3d^7(^4F)4s4p(^3P°) ^6F°_{9/2}$

this means 7 3d electons couple to form a $^4F$ grandparent term

the 4s and 4p electrons couple to form a $^3P°$ parent term and 

the grandparent and parent terms couple to form the final $^6F°$ term.

The above is one of several example given at the NIST page Notations for Different Coupling Schemes