From Traderpedia

Gilts is short for gilt-edged securities. They are debt instruments issued by the U.K. government, for a fixed term at a fixed rate of interest, to fund its spending.

[edit] Types of Gilts

A type of gilt is determined by the length of time before it's maturity, as so:

• Shorts - less than 5 years
• Mediums - 5 to 15 years
• Longs - more than 15 years