This is probably one of the shortest posts here.
Whenever I do online research for genealogies I am often baffled at how sweeping many people are in describing their or other people's genealogies. I hope this post will help others who are doing family history research learn the correct terms to use to describe their family members.
The word ancestor may be interchanged with the word ascendant. Both words refer to the point of origin of a certain person of a family. Example: Martin Co is the ancestor of President Cory Aquino, or, An ascendant of President Cory Aquino is Martin Co. Another term that may be used (but which I do not recommend) is progenitor.
Obviously, if the root is an ascendant, the succeeding generations are "descendants", such that The Cojuangco clan of Tarlac can be traced to a common ancestor, Martin Co. His descendants include President Cory Aquino and Danding Cojuangco.
We also need to address the use of ancestor or descendant when we describe certain people in history. Some web articles have discussed that former president Gloria Macapagal-Arroyo is a descendant Gen. Lazaro Makapagal, one of the soldiers tasked by President Emilio Aguinaldo to execute Andres Bonifacio. While I understand the rationale behind this comparison and correlation between the murderer of a popular revolutionary symbol and the hated former president, we must be very clear about the terminology used here. PGMA is NOT a descendant of Lazaro Makapagal. While both can probably be traced to Don Juan Macapagal (a great-grandson of Rajah Lakandula), PGMA is in no way a direct lineal descendant of Lazaro. The proper term used by these bloggers should be, at the very least, a "distant relative".
Speaking of descendants. If we wish to claim someone as a descendant of somebody, although the relationship is not direct, the term "collateral descendant" comes in. Here's an illustration: My great-great-great-grandfather's name is Don Jose Francisco Lucero y Cabrera. His younger brother was Don Matias Lucero y Cabrera. I am a direct descendant of Don Jose Lucero, while I am a collateral descendant of Don Matias Lucero.