When governments borrow – by selling ‘gilts’ in the UK and ‘treasuries’ in the US – they offer the buyer a low annual return or ‘yield’, as the risk of default is virtually non-existent. Companies that borrow by issuing bonds, on the other hand, have to offer a higher yield to attract investors who are worried about the higher risk of non-repayment and the potential loss of their investment.

The gap between the higher return offered by a corporate bond and the ‘risk free’ return on a safer government bond is known as a ‘spread’. The riskier the company, the bigger – or ‘wider’ – this credit spread will be. So if the yield on gilts is 5.5% and a safe AAA rated firm offers a yield of 5.7%, the spread of 0.2% is said to be ‘narrow’ – or small. Conversely, a firm with a lower credit rating and a higher risk of default might have to offer a return of, say, 6.5% with a correspondingly wider spread of 1% over safer gilts.

• Watch Tim Bennett’s video tutorial: What are credit spreads?