胡桃（英语：pecan），俗称核桃、羌桃、合桃，为胡桃科胡桃属（学名Juglans）植物的统称，原产于中亚地带。

叶边缘锯齿状，花为穗状花序，有树脂，小枝中空，内有片状髓心，雌雄同株。坚果大，肉质的绿色外壳（通称果皮）包被住坚果，其汁液见空气后，氧化变黑色，所以如果用手去掰果皮，会使手沾黑，不容易洗掉，但干燥后肉质外壳就会变成纤维状。绿色“果皮”内部是种子，通称坚果，种皮通称核桃壳，其子叶肉质多油，通称核桃仁。

Walnut trees are any species of tree in the plant genus Juglans, the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves 200–900 millimetres (7.9–35.4 in), with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts (Pterocarya), but not the hickories (Carya) in the same family.