A spiro compound is an organic compound that has two or more rings (a ring system), in which 2 and sometimes 3 rings are linked together by one common atom, examples of which are shown at right.The simplest spiro compounds are bicyclic (or have bicyclic portion as a part of the larger ring system); in such bicyclic spiro compounds, two rings are connected through the one common atom. The one common atom connecting the participating distinguishes them from fused ring compounds that have two rings linked by two adjacent atoms, and from bridged ring compounds that have two rings linked by two non-adjacent atoms.