Semantics may be implicit, existing only in the minds of the humans who communicate and build Web applications. They may also be explicit and informal, or they may be formal. The further we move along the continuum, the less ambiguity there is and the more likely it is to have robust correctly functioning Web applications. For implicit and informal semantics, there is no alternative to hardwiring the semantics into Web application software. In the case of formal semantics, hardwiring remains an option, in which case the formal semantics serve the important role in reducing ambiguity in specifying Web application behavior, compared to implicit or informal semantics. There is also the new possibility of using automated inference to process the semantics at runtime. This would allow for much more robust Web applications, in which agents automatically learn something about the meaning of terms at runtime.