Rough endoplasmic reticulum (RER), is a network of interconnected flattened sacs that is an organelle with a continuous membrane found in the cytoplasm of eukaryotic cells and is essential for protein synthesis.
Rough and smooth ER is found in both plant and animal cells.
Ribosomes, which are small, globular organelles that make those proteins, are set up in the rough endoplasmic reticulum.