Lens can refer to telescope optics or gravitational light deflection from distant galaxies. Read on for more.
Lens (def. 1): In the context of gravitational light deflection, lens means a distortion and magnification of light from distant galaxies created by the gravitational field of a huge amount of matter, like a cluster of galaxies.
Lens (def. 2): In the context of a telescope, lens can refer to the telescope optics that reflect and focus the image or the eyepiece lens that magnifies that image.