Which one of the following sections of the Transfer of Property Act defines 'Notice' ?

Notice is defined in section 3: "a person is said to have notice of a fact when he actually knows that fact, or when, but for wilful abstention from an enquiry or search which he ought to have made, or gross negligence, he would have known it".

Explanation II to section 3 only adds one form of constructive notice, through actual possession; it is not the definition itself. Section 2 is the repeal and savings clause, and section 5 defines transfer of property.