The left-hand side (literally the left of the two numbers) in a two-way price quote is the bid. It indicates the highest price at which a dealer, investor or market maker is willing buy at.
E.g. if AUD/USD = .9310/15, to take the left-side you would sell the AUD at .9310.
The difference between the left and the right hand side of a two-way price quote is the spread.