An orange was a citrus fruit native to Earth. It was enveloped by an orange-colored rind or peel which was generally removed prior to consumption of the fruit. The juice of an orange was used to make a beverage called, aptly enough, orange juice.
Also in 2270, an orange was among the fruit on a platter on the dining table on the USS Enterprise. Later, oranges were among the items that the food synthesizer spat out at Montgomery Scott. (TAS: "The Practical Joker")
When the USS Enterprise was bombarded by an energy beam after encountering a crystalline planet in 2269, Montgomery Scott reported that the starship's dilithium crystals were "unpeeling like the rind of an orange." (TAS: "The Terratin Incident")