What is The scientific definition of SER?

The definition I believe you are looking for is Smooth Endoplasmic Reticulum. Unlike RER (Rough Endoplasmic Reticulum the SER does not contain ribosomes. Depending on the area, SER has different roles. The SER has increased surface area for the action or storage of key enzymes and their products. Foe example, SER in muscle cells serves to store calcium. SER in liver cells contain enzymes needed to detoxify drugs (just to name a few).