What does the word "exist" mean as applied to God's existence and the creation?

Nearly all doctrines of creation refer to the word "exist" or "existence" as if all readers knew its meaning. However, if the significance of creation (and the very nature of God) depends on the word "exist", should it really be taken for granted that the hearer or reader automatically knows what this term means? Factually, what does the word "exist" mean? If there are multiple assigned or possible meanings, what is an overview of Christian doctrines as to its meaning? Without resorting to any circular definition, what does it mean when applied to various claims about *creation*, *being*, and the nature and existence of God? For example, when a Christian says that God is "self-existing", what does that phrase mean (again, without any circular definition)? For example, I can refer to a dictionary that says "exist" means "to have actual being; to be real" (American Heritage 5th ed.). Then I look up "be" and Oxford languages says it simply means "exist". Clearly we are missing something. What does "exist" mean, when used in the context of creation or the nature of God? One reason why this question is not purely philosophical is that special pleading is often applied to God and the creation under various theories of theology. For example, many people assert that God "caused causality" or that it "makes no sense" to ask about how God came to be God. If that is so, and if it is a purely philosophical argument, then it wouldn't matter that the subject is God; the exact same logic should apply to any other being or article such as a shoe, but it doesn't. Therefore the special pleading regarding the existence of God and the nature of creation must be addressed within a theological framework or else reconciled on genuine and general philosophical and factual basis. These exceptions must be addressed; no self-respecting philosopher will accept absurdities or special pleading as obviously true. What is meant when Christians say that God caused things to exist through Creation, or that God is self-existing?