XAUUSD is the price of one troy ounce of gold in US dollars, the benchmark gold quote from which every other XAU cross is derived. A quote of 3,400.00 means $3,400 per ounce.
On the standard MetaTrader contract 1.00 lot is 100 troy ounces, so a .00 gold move is about 00 per lot and a 0.01 lot is one ounce. Typical retail spreads run $0.15 to $0.40 and widen sharply at the 21:00 to 22:00 UTC rollover and around US data.
The best XAUUSD windows are the London open (07:00 to 09:00 UTC) for range expansion and the London to New York overlap (13:00 to 17:00 UTC) for the deepest liquidity, when US CPI, Non-Farm Payrolls and FOMC releases land.