Molecular fingerprints are a way of encoding the structure of a molecule. The most common type of fingerprint is a series of binary digits (bits) that represent the presence or absence of particular substructures in the molecule. Comparing fingerprints allows you to determine the similarity between two molecules, to find matches to a query substructure, etc.
Open Babel provides several fingerprints of different types:
The next two sections describe the Fingerprint format and Spectrophores in depth. For the others, see the relevant sections listed above.