Is the Ocean Samadhi a metaphor or an actual meditation? In Huayen related documents I see the phrase "ocean samadhi" a lot. (also ocean mirror samadhi, ocea seal samadhi) Here is one source:


  Huayan teaching features a range of holographic samadhi instructions
  drawn from the Flower Ornament Sutra. These practices help clear away
  limited preconceptions, foster fresh perspectives on reality, and
  expand mental capacities by expressing our deep interconnectedness.
  
  ... Another model is the
  "ocean mirror" or "ocean seal" samadhi. In this image, awareness is
  like the vast ocean surface, reflecting and confirming in detail all
  phenomena of the entire universe. Waves of phenomena may arise on the
  surface of the ocean, distorting its ability to mirror plainly. But
  when the waves subside as the water calms and clears, the ocean mirror
  again reflects all clearly. Our individual minds are like this, often
  disturbed by turbulence, but also capable of settling serenely to
  reflect clear awareness.
  
  Ref.


I searched Cleary's Avatamasaka translation and only found the word Ocean used as a metaphor or simile. (The kindle stops searching at 500 hits, well before the end of the book)

Anyhow, can't tell if this is a sort of visualization exercise, literally involving thinking about waves and the ocean, or if this is just a metaphor for the meditative states achieved in samyak-sam-bodhi.
The waves and the ocean metaphor are found in several places in the Lankavatara Sutra where the storehouse consciousness is said to be like the ocean and the waves are like the other seven consciousnesses, so I think the term Ocean Samadhi most likely refers to the state in which the other seven consciousnesses cease.