It may be a specific "chart" or "piece" for rhythm games (like Clone Hero or Chorus ), where individual songs or assets are often archived in numbered batches for easier distribution.
Downloading .rar files from unverified sources can pose a security risk. If you are looking for this file specifically, it is best to check the original community or forum where you first saw the reference. 151.rar
The phrase does not refer to a widely known single file or software package in general public records. It may be a specific "chart" or "piece"