Wobble base pair
A wobble base pair is a G-U and I-U / I-A / I-C pair fundamental in RNA secondary structure. It has comparable thermodynamic stability of the Watson-Crick base pair. Wobble base pairs are critical for the proper translation of the genetic code. The genetic code makes up for disparities in the number of amino acids (20) for codons (64) by using modified base pairs in the first base of the anti-codon. One important modified base is inosine which can basepair with three bases including uracil, adenine, and cytosine.
Another critical base pair is the G-U base pair which allows uracil to base pair with two bases: guanine and adenine.
Links
Nature on Wobble base pair (http://www.nature.com/cgi-taf/DynaPage.taf?file=/embor/journal/v1/n1/full/embor635.html)