Processed meat is considered to be any meat that has been modified in order to either improve its taste or to extend its shelf life. Methods of meat processing include salting, curing, fermentation, smoking, and the addition of chemical preservatives. Processed meat is frequently made from pork or beef, but also poultry and others. It can contain meat by-products such as blood. Processed meat products include bacon, ham, sausages, salami, corned beef, jerky, hot dogs, lunch meat, canned meat, chicken nuggets, and meat-based sauces. Meat processing includes all the processes that change fresh meat, with the exception of simple mechanical processes such as cutting, grinding or mixing.

Meat processing began as soon as people realized that cooking and salting helps to preserve fresh meat. It is not known when this took place; however, the process of salting and sun-drying was recorded in Ancient Egypt, while using ice and snow is credited to early Romans, and canning was developed by Nicolas Appert who in 1810 received a prize for his invention from the French government. Medical health organizations advise people to limit processed meat consumption as it increases risk of some forms of cancer, cardiovascular disease, and Alzheimer's disease.

The American Institute for Cancer Research and World Cancer Research Fund define processed meat as "meat preserved by smoking, curing or salting, or addition of chemical preservatives".

The Encyclopedia of Meat Sciences defined processed meat as "any meat preserved by smoking, curing, or salting, or with the addition of chemical preservatives; examples include bacon, salami, sausages, hot dogs or processed deli, or luncheon meats".

Nitrate and sodium nitrite found in processed meats can be converted by the human body into nitrosamines that can be carcinogenic, causing mutation in the colorectal cell line, thereby causing tumorigenesis and eventually leading to cancer. Processed meat is more carcinogenic compared to unprocessed red meat because of the abundance of potent nitrosyl-heme molecules that form N-nitroso compounds.

A principal concern about sodium nitrite is Nitrosation/nitrosylation, the formation of carcinogenic nitroso-compounds in meats containing sodium nitrite or potassium nitrate, especially nitrosyl heme. In addition to nitrosyl-haem, carcinogenic nitrosamines can be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats.

Nitrate and nitrite are consumed from plant foods as well as animal foods, with 80% of a typical person's nitrate consumption coming from vegetables, especially leafy and root vegetables such as spinach and beets. Some nitrate is converted to nitrite in the human body. Nitrate and nitrite are classified as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration, and are not directly carcinogenic. Yet, when nitrate or nitrite interact with certain components in meat, such as heme iron, amines, and amides, they can form nitroso compounds, which may contribute to the association between consumption of processed meats and higher incidence of colorectal cancer.

The International Agency for Research on Cancer (IARC) at the World Health Organization (WHO) classifies processed meat as Group 1 (carcinogenic to humans), because the IARC has found sufficient evidence that consumption of processed meat by humans causes colorectal cancer.