A single-stranded RNA molecule containing about 70-90 nucleotides, folded by intrastrand base pairing into a characteristic secondary ('cloverleaf') structure that carries a specific amino acid and matches it to its corresponding codon on an mRNA during protein synthesis.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 167 (https://doi.org/10.1351/pac199264010143)