An lzw file extension is related to the Lempel-Ziv-Welch compressed archive format.
LZW file extension - LZW compressed archive
What is lzw file? How to open lzw files?
File type specification:
The lzw file extension is used for archives compressed with the LZW compression method.
The compression format LZW is Lempel-Ziv-Welch or LZW compression.
Basically LZW creates tables of strings while compressing/decompressing data, and then later outputs the ID of the string rather than the string itself saving space. Decompression reads this and it to build a table of strings as it reads, saving the compression from needing to write large string tables at the beginning of the file, thus making it very effective.
This lzw file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.