Evasive means tending or seeking to evade; elusive; intentionally vague or ambiguous. The reason for evasiveness may be to avoid something unpleasant. When a pleading requiring response is evasive, the other party can ask the court to order for a unambiguous and definite pleading.
“A party may move for a more definite statement of a pleading to which a responsive pleading is allowed but which is so vague or ambiguous that the party cannot reasonably prepare a response. The motion must be made before filing a responsive pleading and must point out the defects complained of and the details desired”, [USCS Fed Rules Civ Proc R 12.]