Business letters are a formal way of communicating with other businesses or individuals. The following abbreviations are commonly used in business letters: ENC (3 letters) stands for Enclosure, RE (2 letters) stands for Regarding, INC (3 letters) stands for Incorporated, ULT (3 letters) stands for Ultimate, ATTN (4 letters) stands for Attention, ENCL (4 letters) stands for Enclosed, and INST (4 letters) stands for Institute. These abbreviations are used to make the letter more concise and easier to read.