TALENs, or Transcription Activator-Like Effector Nucleases, are a type of engineered nuclease used in gene editing. They are composed of a DNA-binding domain derived from transcription activator-like effectors (TALEs) and a DNA cleavage domain, typically from the FokI endonuclease. TALENs can be designed to target specific DNA sequences, allowing for precise editing of the genome.