Bacon was a type of food that came from the meat of a pig.
In 2267, Pavel Chekov ordered a sandwich with swiss cheese and bacon as part of his meal. Because of a computer malfunction, he received a chicken sandwich instead. (TOS novel: Web of the Romulans)
While discussing the idea of an inflatable rubber starship with Commander Montgomery Scott, Captain James T. Kirk ordered a breakfast of two eggs sunny side up, crisp bacon, wheat toast and a large orange juice. (TOS novel: How Much for Just the Planet?)
One morning in 2268, Leonard McCoy told Christine Chapel he was going to have bacon with his breakfast, but he in fact did not. (TOS novel: Cloak)
Curzon Dax once told a young Benjamin Sisko that Klingon ships smelled of bacon, beer and oil. (DS9 - The Left Hand of Destiny novel: Book Two)
Gretchen Janeway, mother of Kathryn Janeway, was a traditionalist when it came to cooking. She raised Kathryn to use a toaster to get the right texture needed for a bacon, lettuce and tomato sandwich. (VOY - Distant Shores short story: "Isabo's Shirt")
Tom Paris enjoyed eating bacon. In 2374, Seven of Nine helped herself to the serving of bacon that Tom had on his plate. (VOY - String Theory novel: Cohesion)