A storeroom was a place where supplies were kept.
In 2264, the USS Enterprise stored bottled Vulcan emotions in a storeroom prior to transporting them to Beta IV. Although the room was labeled off-limits, the door was opened by Yeoman Pandora Trask, freeing the emotions. (TOS comic: "The Brain Shockers")
In the 2260s, pirate captain Kandok commandeered the USS Enterprise and took Nyota Uhura hostage. Kandok's rebel crew locked James T. Kirk and Spock in a storeroom. Kirk quickly loosened a ventilator grill cover. They escaped by crawling through the ventilation shaft, eventually making it to his quarters. (TOS comic: "Planet of Rejects")