A Nissl body is also known as Nissl or tigroid substance.
It is a large granular body found in neurons.
Nissl's granules are present in the cytoplasm of the cell body of the neurons along with other cell organelles like the Golgi apparatus, endoplasmic reticulum, mitochondria, nucleus, etc.
These granules give a slightly coloured appearance to the cytoplasm of the cell body.