DIBBS is where the Defense Logistics Agency posts most of its own solicitations and requests for quote, mainly for spare parts, supplies, and similar items DLA buys constantly. It runs alongside SAM.gov rather than instead of it, DLA opportunities are typically synopsized on SAM.gov too, but the actual bidding and quoting for a lot of DLA work happens inside DIBBS itself. If parts or supply work for the military is your market, checking DIBBS directly is worth doing rather than relying on SAM.gov alone.

In a sentence

"Quotes for this item must be submitted through DIBBS by the closing date shown." SAM.gov might be where you first saw the notice, but DIBBS is where you actually have to go to submit anything.