Lensing is the bending of light by gravity. A particularly massive object, like a galaxy with a massive halo, acts as a lens, distorting the images of other galaxies at higher redshift that fall behind or near it. The practical side of this is that a lensed object has the same surface brightness as when it was unlensed, but subtends a larger angular size. As a result, it's integrated flux is higher. Amplifications can be as high as 100 or more times.
Lenses are in many cases the only way to study certain objects at high redshift.
CO studies at high redshift, for example, are confined primarily to lensed objects like FSC 10214 and the Cloverleaf Quasar, because without lensing no telescope is sensitive enough to make the observations. On the one hand, we may directly target several clusters that are known to contain giant gravitational arcs. In these cases, we will definitely detect the arcs. However, the more interesting case will be the discovery of serendipitous lenses in the primary survey data. There is no way from the WIRE data alone to determine if a galaxy is lensed or not.