The symantics of a language is the proper structure of the language. From Dictionary.com:
se�man�tics 1. The study or science of meaning in language. 2. The study of relationships between signs and symbols and what they represent. 3. The meaning or the interpretation of a word, sentence, or other language form: We're basically agreed; let's not quibble over semantics.
And if you were looking for examples of symantical errors, just listen to Gee Dubwa for a couple of minutes. Good Luck, -Dirk Schreckmann