Credit investors often talk in euphemisms. The safest bonds, with the highest credit ratings and hence the lowest yields, are almost always referred to as “high-grade” rather than “low-yield”. Conversely, the riskier stuff, where defaults are more likely, is politely dubbed “high-yield” rather than “low-grade”. Recently, though, the yield on supposedly high-yield bonds has not been all that high.
Source: Finance - economist.com