The general difference between PubMed and MEDLINE is that MEDLINE is the curated collection of citations of articles articles published in journals, which have been approved by the National Library of Medicine (NLM) and have been indexed by the NLM to have MeSH terms associated with those articles.

Whereas PubMed includes MEDLINE, along with other articles which are in the categories of:

  1. In-process citations which haven't been approved by the NLM or indexed with MeSH terms
  2. Citations to articles which are published in NLM approved journals, but whose scope it outside the life-sciences (e.g. an Physics article published in Nature).
  3. Citations of ahead of print articles in journals approved by the NLM, but not yet indexed
  4. Citations to articles in journals before the journal was approved by the NLM
  5. Pre-1966 citations which have not been indexed with MeSH terms
  6. Citations to articles submitted to PubMed Central which are qualitatively reviewed by the NLM, but not as in-depth as other articles.
  7. Citations to articles published by NIH funded researchers
  8. Citations to books available on the NCBI Bookshelf

For more information, visit NLM's description of the difference.