Picking up on this, you can say that over-the-board chess is pretty much Black and White - no consultation with or assistance from external sources during the game. If you needed too, you could eliminate all possibilities of outside help by playing under supervision in a sealed room without live spectators.Christopher Kreuzer wrote: I could well believe that some people could be tempted to cheat in online chess who wouldn't dream of doing so over the board.
Correspondence style chess is much greyer. It's usually regarded as OK to consult published works or to research previously played games. Even private third party analysis might be accepted. Beyond that, asking opinions of third parties, or using computer engines even just for blunder checks is usually frowned upon at best and a cause for banning otherwise.
Compare that though with the now mostly obsolete practice of adjournment. Here almost anything goes in the OTB break of game, engine analysis, tablebase lookups, consultations with the team's GM trainer etc.