«القضية قول يحتمل الصدق والكذب»
A proposition is a statement capable of being true or false.
Capability of truth or falsity means that the statement has the kind of content whose correspondence with reality can be assessed. It does not mean the same definite proposition must actually be both true and false; rather, a particular proposition may be true or false and is open to such evaluation.
“Zayd is present” is a proposition because we can investigate whether he is actually present.