I have been writing many philosophical posts on this site for a while. When I have asked various people what philosophy was they have given different answers. It is one of those few questions in which the experts in a topic do not agree on what the topic is. So it is not a simple question to answer. We can begin to answer the question by starting with what the philosophical experts do agree on. There are two of those things. First, the experts agree that certain topics are philosophical ones. Second, the experts agree that certain people are philosophers.
Let’s begin with the topics of philosophy. Philosophers generally agree that certain topics are philosophical. These include ethics, general questions about the nature of knowledge and reality, human nature, the place and method of reasoning as well as a general understanding of what science, psychology, history, theology and other related disciplines are. Now this agreement does not extend in all directions. Some philosophers believe that empirical studies should inform us about the way the world is. Therefore, they reject any philosophy that claims to have general knowledge about reality apart from empirical information. Other philosophers believe that the narrow and technical claims of some modern philosophers are not really philosophy. They fail to deal with the wide scope of human experience. They also believe that the details of logic and related technical matters are not philosophical for the same reason. Finally, there have been those who have participated in philosophical discussions and produced philosophical works but have claimed that they were not philosophers. They have claimed that they were not philosophers because they did not limit themselves to reason but added in revelation (the Bible) as well.
This is a nice place to jump off into philosophers. There are two ways to count someone as a philosopher. One way is by claiming that a person can competently produce philosophical work and understand philosophical work. The other way demands that philosophers also self-identify as philosophers. If we use the first way to count philosophers, then many people may be counted that would be unexpected. There are many religious believers who do philosophy as a part of their religion. This is true not only in Medieval Christianity but also in India and China. The list of Western names (since I am not familiar with much Eastern philosophy) includes such people as Plato, Aristotle, Aquinas, Descartes, Hume and all of the other people taught in various philosophy courses. We might not all agree on who is a good philosopher and who is a horrible incompetent one, but we agree that these are all philosophers none the less.
By examining these things that we agree on, we can determine what philosophy is in a general sense. We just look for what these people and subjects have in common. We pay particular attention to what the various debates over philosophy assume about philosophy itself. This is just a start.