Tax-to-GDP ratio represents the size of a country's tax kitty relative to its GDP. It is a representation of the size of the government's tax revenue expressed as a percentage of the GDP.
Higher the tax to GDP ratio the better financial position the country will be in. The ratio represents that the government is able to finance its expenditure. A higher tax to GDP ratio means that the government is able to cast its fiscal net wide. It reduces a government's dependence on borrowings.