An indirect quote is the reciprocal of a direct-quote. For a UK resident, GBP/USD at 1.2700 is indirect: it says what one pound fetches abroad. Sterling, the euro, the Australian dollar and the New Zealand dollar are quoted this way against the dollar by market convention, which is why they are sometimes called the commodity-style or certain-for-uncertain quotes.
The two forms carry identical information. One is simply 1 divided by the other, before spreads.
Example: GBP/USD trades at 1.2700. The equivalent direct quote for a British reader is USD/GBP = 1 / 1.2700 = 0.7874, meaning one dollar buys about 79 pence.
Related: direct-quote, cable, currency-pair-notation, cross-rate