I see it used to mean a specific group of people for a specific period of time, yet I also see it used to refer to the descendants of groups, so people talk of Egyptian Civilization and feel fine referencing every dynasty up to the Arab invasion, and I see other ideologically motivated people talk of "western" civilization and use it to include pretty much every group that is seen to be an ancestor of a community as well, while at other times the term "previous civilization" is used to contrast a community with its own descendents, or to ascribe one set of accomplishments to one group of people without giving any sort of credit to the following generations...
How do historians deal with things like cultural continuity, or how do they talk about values that get passed on generationally that tie a people to their descendents - or do they somehow limit themselves to material culture without acknowledging philosophical continuity, or is this only really commonly acknowledged in situations like tracing the threads of "Democracy" or similar ideas?
I am coming at this question from a pedagogical angle, so I apologize if I have missed the point.
At our institution World History is divided into two introductory level courses; the world pre-1500 and the world post-1500. One of the first things I do at the pre-1500 level course is discuss the idea of terminology. Whether we define and discuss the labeling of dates (BP, BC/AD, BCE/CE) or words we might encounter, like civilization. I usually turn students loose for a bit to research all the different definitions of that word that they can find in order to understand what it really means and how it can be used.
The point of the exercise is to look at how the word is defined in order to understand how and why it has been used to ascribe civilization to some people but not to others. There are always good definitions and bad definitions, but the take away is that our definition of civilization, determines who is worthy of examining as a 'civilization.' Even though this question is posed in a class centered on ancient societies, it's an important point from which we can also talk about early archeology and how history was constructed in the nineteenth or early twentieth century. I tend to use the terms 'society' or 'culture' depending on the particular unit or thing we are trying to describe at a moment in time; though if we are talking about a specific political unity then it makes more sense to describe it as such (kingdom, empire, etc).
The textbook I used to use and sometimes still recommend to students who like having a reference guide to the course is "Traditions and Encounters." Jerry Bentley, one of the original authors/editors and long time guiding light at the Journal of World History, framed history around the idea of continuity and change-- or traditions and zones of encounter. The idea of framing history this way was to draw out those lines of thought or practice that descend down through history, while also taking account of traditions as not static. They change and adapt to different circumstances and can be entirely reinterpreted when carried into a new context.
The textbook is still a textbook-- limited by the format and desire to present a coherent easy to read narrative of history-- but I always found it a useful way to frame the past in the course and often approach material through the lens of traditions and changes (or vice versa). The textbook generally focuses on geographic regions rather than discreet "civilization" units and includes overviews of regions of contact, especially trade routes and maritime basins (which was the focus of Bentley's research).
I prefer this approach to other books that present each chapter as a "civilization" that can be studied in a vacuum as something static and unitary-- especially when those books don't include places such as the Pacific which has the unintended (or subconscious) effect of placing the Pacific as a place outside of, or without, civilization. It can also lead to entanglements, such as some of the ones I think you hint at, where civilization becomes synonymous with nation and inseparable from a nationalistic history that views a particular group of people as having a claim to land or space from time immemorial due to the static presentation of the 'civilization' as a discrete unchanging unit (one that always continues or is replaced).