"Metabolomics is the large-scale study of small molecules, commonly known as metabolites, within cells, biofluids, tissues or organisms. Collectively, these small molecules and their interactions within a biological system are known as the metabolome." European Bioinformatics Institute: What is metabolomics?
"Metabolomics is a newly emerging field of "omics" research concerned with the comprehensive characterization of the small molecule metabolites in biological systems. It can provide an overview of the metabolic status and global biochemical events associated with a cellular or biological system." Metabolomics Society: Metabolomics
"What is metabolomics? Oh, that's easy. It's the study of the metabolome. Very good. Now, what is the metabolome?
Ergo, metabolomics is the study of the complete collection of metabolites present in a cell or tissue under a particular set of conditions (= the metabolome) generating a biochemical profile. It's 'omics for the small molecules." Of Terms in Biology: Metabolomics and Metabonomics by Merry Youle.