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.
When Sub-commander T'Pol tried to take command of Enterprise NX-01 she mentioned her superior authority. Trip Tucker compared her arguments to apples and oranges and reminded her that she was an observer on this mission and Enterprise an Earth ship. (ENT: "Broken Bow")
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")