Used to describe someone who is very thin, often in a derogatory sense.
El gato flacuchento merodeaba por el vecindario en busca de algo para comer.
The scrawny cat was roaming the neighborhood in search of something to eat.
El perro flacuchento parecía tener hambre, ya que sus costillas eran visibles.
The scrawny dog looked hungry, as its ribs were visible.