Refers to the hard outer covering of an egg, typically a chicken egg.
卵の殻を割って中身を取り出す。
Crack the eggshell and take out the contents.
卵の殻は細かく砕いて肥料に使える。
Crushed eggshells can be used as fertilizer.
Compound of 卵 (tamago, 'egg') + の (no, possessive particle) + 殻 (kara, 'shell').