The verification theory of meaning aims to characterise what it is for a sentence to be meaningful and also what kind of abstract object the meaning of a sentence is. A brief outline is given by Rudolph Carnap, one of the theory's most prominent defenders:
If we knew what it would be for a given sentence to be found true then we would know what its meaning is. [...] thus the meaning of a sentence is in a certain sense identical with the way we determine its truth or falsehood; and a sentence has meaning only if such a determination is possible. [4: 420]
In short, the verification theory of meaning claims that the meaning of a sentence is the method of its verification.