What's the difference between a flat-file cabinet and a lateral file cabinet?

These are completely different products for completely different document sizes. A lateral file cabinet has deeper, narrower drawers (2"–4" deep) for hanging letter/legal folders in a side-to-side orientation. A flat-file cabinet has very wide, very shallow drawers (1"–2" deep) designed to store oversized documents — architectural drawings, engineering plans, maps — lying completely flat without folding or rolling. If you're asking the question, it's likely you need both. FindOfficeFurniture.com carries both product types — call 888-719-4960 to confirm which is right for your documents.