Professor David Porteous explains that a translocation is the relocation of part of one chromosome to a another chromosome.
Translocation, if we break down the word, means "trans" - across, and "location" - place. So what that means for a human geneticist or a cytogeneticist, is that there has been a breakage and rejoining of two bits of the human genome in the form of chromosomes. So, to give you a specific example, if we have a translocation between human chromosomes 1 and 11, that means there's been a break on human chromosome number 1 and a break on human chromosome number 11; and a bit of chromosome 1 has transferred to the chromosome 11, and the reciprocal event a bit of chromosome 11 is transferred to the chromosome 1. That, in essence, is what we mean by a translocation.