Illustrated Glossary of Organic Chemistry

Tetrahydrofuran (THF): A five-membered heterocyclic ring consisting of four carbon atoms and one oxygen atom, or a molecule containing this ring. Also the nonpolar aprotic solvent of molecular formula C4H8O containing this ring.

General tetrahydrofuran ring.   
THF, a nonpolar aprotic solvent.
The tetrahydrofuran ring of 2-deoxyadenosine,
a DNA nucleoside, is shown in red.