Belief: What one thinks is true, what one holds is more probable than not. Fundamental propositional attitude.
In discussing human beings, one cannot do without a term like "belief", if only because one knows people have all manner of ideas that may or may not be true, and that other people may agree or disagree about these assessments. It should be noted that the inclusion of probability makes the analysis of beliefs both more subtle and realistic and more complex.
And apparently it takes considerable intellectual sophistication, especially in matters of ideology or religion, to know that what one believes, however fondly or passionately, is usually at best more probable than not, and not provably strictly or completely true.