An LZH file is an archive compressed using Lempel-Ziv and Haruyasu (LZH) compression algorithm. It contains one or more files that have been compressed to reduce their file size for the purpose of saving storage space and transporting them to another location. LZH archives are similar to LHARC compressed archive (.LHA) archives.

LZH is derived from the Lempel–Ziv–Storer–Szymanski (LZSS) compression scheme developed in the 1980s, but it features extended compression using dynamic Huffman coding. The LZH acronym comes from the names of the inventors Lempel-Ziv and Haruyasu. LZH compression is most commonly used in Japan but is supported by a variety of compression and decompression utilities, such as Corel WinZip, WinRAR, and 7-Zip. You are most likely to encounter LZH files if you use a compression utility that supports the format and compress your files with the LZH scheme. However, you may also receive an LZH archive from a co-worker or friend via email or cloud storage space that is looking to share one or more large files.