Which type of bond characterizes an unsaturated compound?

An unsaturated compound is defined by the presence of at least one double or triple bond between carbon atoms. These types of bonds reduce the number of hydrogen atoms that can be attached to the carbon chain compared to saturated compounds, which only contain single bonds and are fully "saturated" with hydrogen.

The existence of double or triple bonds allows unsaturated compounds to participate in reactions that saturated compounds cannot, leading to greater reactivity. This characteristic is crucial in organic chemistry as it influences the properties and applications of these compounds.

In contrast, single bonds alone define saturated compounds, and ionic bonds are unrelated to the saturation of organic compounds. Thus, the defining feature of unsaturated compounds is indeed the presence of at least one double or triple bond, which makes option C the correct response.