Ārammana: Object. There are six: visible object, sound, odour, taste, body-contact, mental-object. The mental-object dhammārammana may be physical or mental, past, present or future, real or imaginary. The 5 sense-objects belong to the materiality-group rūpa-khandha see: khandha. They form the external foundations for the sense-perceptions, and without them no sense-perception or sense-consciousness seeing, hearing, etc. can ever arise.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.