A government bond yield is the annual return an investor earns for lending to a government for a given term. The 10-year yield is the standard benchmark for long-term borrowing costs.
German Bund (10Y) — the eurozone's safe-asset benchmark; other countries are judged against it.
Sovereign 10Y yields — the equivalent for individual countries, in euros.
Local-currency yields — for EU members outside the euro, in their own currency.
Spreads tell the story
The gap ("spread") between a country's yield and the Bund reflects the extra risk investors demand. Widening spreads — as in the 2010-2012 sovereign debt crisis — signal stress; narrow spreads signal confidence. Yields also set the cost of carrying government debt, which is why they matter so much for highly indebted states.
Source: ECB / national benchmarks, daily.