A bond's yield is what it pays relative to its price. Prices and yields move opposite: if new bonds pay more, nobody pays full price for an old one paying less, so its price falls until the two match. The yield curve plots yields of government bonds from short to long maturity. Normally longer bonds pay more. When short-term yields rise above long-term, the curve is 'inverted,' which has often come before recessions and is watched for that reason.