Real yield is the nominal yield minus expected inflation. A bond paying four per cent while inflation runs at five has a negative real yield: the coupon arrives on time and buys less than the money that bought the bond.
The US market prices it directly through Treasury Inflation-Protected Securities. The gap between a nominal Treasury and the matching TIPS is the breakeven inflation rate, a live reading of what the bond market expects prices to do.
Real yields are the key variable for gold and for long-duration equities. Gold pays no income, so it competes most poorly when real yields are high and most successfully when they are negative, which explains moves that look disconnected from the inflation headlines themselves.