boundp

(boundp symbol)

Returns t when symbol names a bound global variable (defvar/defparameter/top-level setq), nil otherwise. Like Common Lisp's dynamic-only boundp, lexical bindings (let, function parameters) are invisible. t, nil and keywords are self-evaluating constants, so boundp of any of them is t.

On the compiled backends the check reads the embedded eval runtime's global environment, so using boundp (or symbol-value/fboundp) pulls that runtime into the output like eval does.