The "wobble hypothesis" was proposed by Francis Crick in 1966 as an explanation for how one transfer RNA (tRNA) can recognize two codons.
According to the hypothesis, each tRNA has an anticodon that is a base triplet, and normal base-pairing occurs between the first two bases and complimentary bases in an mRNA codon; the third base has a free play (wobble) that lets it pair with any of a number of bases that are in the third position of different codons.
This writeup is based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/