The concept of __illocutionary acts__ was introduced into linguistics by the philosopher J. L. Austin in his investigation of the various aspects of speech acts. In his framework, ''locution'' is what was said and meant, ''illocution'' is what was done, and ''perlocution'' is what happened as a result- wikipedia 
When somebody says "Is there any salt?" at the dinner table, the ''illocutionary act'' is a request: "please give me some salt" even though the ''locutionary act'' (the literal sentence) was to ask a question about the presence of salt. The ''perlocutionary act'' (the actual effect), might be to cause somebody to pass the salt.