USDA is short for the United States Department of Agriculture. It is the part of the US government that looks after farming and food. It does a lot of different jobs: it gives money and advice to farmers, it checks that meat, eggs and other food are safe and clean, it decides what the labels on food may say (the word "organic" on American food is a USDA rule), it runs food help programs for poor families and school lunches, and it takes care of national forests. Because of the food-checking part, students meet this word most often on packets: you will see a round USDA mark on American meat, or the green-and-white USDA Organic mark. In speech people say the three letters, U-S-D-A, never a word. You will also hear it used as a kind of adjective in front of a noun — "USDA inspected", "USDA grade A eggs", "USDA approved" — and there "USDA" is doing the work of "the government says this is fine". Note that food safety in the US is split: the USDA handles meat, poultry and eggs, while most other food is the FDA's job. Americans themselves mix these two up all the time, so do not feel bad if you do.