Conference just a set of fractions used in odds betting markets. The set does not consist of exact equivalents to chances and all decimal. We use.
For example, compounding chances 30’s exact equivalent is odds 29/1. However 29/1 is not used in betting markets, instead 30/1 is used, so that’s exactly what seems in this converter.
For an explanation of these chances types with this table see decimal, fractional and American odds. To learn what the numbers represent see understand odds as probability with overround.