The "Three Baskets" of the canonical
Buddhist Teachings.
When the sutras representing the Buddha's Teachings were first rendered into written form from mnemonics they were written on palm leaves. These were sewn together into volumes. Since the Buddha taught from the age of 33 until his death at 84, there were a lot of leaves.
The sutras are the first basket.
The second are the Abhidharma Teachings, the "Overarching Teachings" which describe the various components of experience in a staggering number of numbered lists.
The third basket refers to the Vinaya, the various precepts and monastic codes that governed the Sangha.
These are the Sanskrit version of these terms. The Pali are similar but simpler: Tipitika, sutta, Abhidhamma, Vinaya.