What is meant by "frequency bandwidths of 9:1"?

What is meant by "frequency bandwidths of 9:1"? What is mentioned before colon symbol and what is mentioned after colon?

Hello,

This is the ratio between highest an lowest useful frequency. When a wide band balun structure has a useful frequency range of 1 to 9 GHz, they say it has a 9:1 bandwidth.

Some spiral antannes (where the spirals become wider like a snale horn)) have very large bandwidth ratio.