Six sense objects
Ṣaḍāyatana (Sanskrit) or saḷāyatana (Pāli) means the six sense bases (Pāli, Skt.: āyatana), that is, the sense organs and their objects. These are:
Eye and Vision
Ear and Hearing
Nose and Olfaction
Tongue and Taste
Skin and Touch
Mind and Thought
That is, in Buddhism, the sixth "internal" and "external" sense bases are: mind (Skt., manas; Pali, mano); and, thought (along with memory and emotion) (Skt., dharma; Pali, dhamma).
Related Buddhist concepts
Ṣaḍāyatana is the fifth link in the Twelve Nidānas of Pratitya-Samutpada (Dependent Origination) and thus likewise in the fifth position on the Bhavacakra (Wheel of Becoming). Ṣaḍāyatana (Sense Gates) is dependent on Nāmarūpa (Name and Form) as condition before it can exist.
"With Name and Form as condition, Sense Gates arise".
Ṣaḍāyatana is also the prevailing condition for the next condition in the chain, Contact (Sparśa).
"With|Sense Gates as condition, Contact arises".