The word ego can have different meanings for different people. Here, and in most spiritual teachings, ego means identification with form - any form - a thought form, emotional form or physical form. This is where the human dysfunction lies, and most of our pain arises.
This identification with form gives rise to a false identity, a false sense of self. It is often referred to (particularly in buddhism) as the illusory self. It is a mental construct that you identify with. To identify with something means that you believe it is who you are.
This false sense of self is also referred to as the egoic self, and often is called "the ego".
Who you are then becomes conceptual. The term "I" then becomes a concept. You believe that form makes up who you are - your thoughts, emotions, name, body, possessions etc. are all invested with a sense of self, a sense of "I".
You then have a voice in your head that does not stop talking, judging, commenting on everything that happens, did happen or might happen. Life becomes completely conceptual, and you believe that the "voice in the head" (or sometimes "voices") is who you are. "This is me talking" says the voice in the head.
Who you think you are then basically consists of a bundle of mental-emotional thought patterns that have been conditioned by the past, looking to the future for relief of it all.
