Non-Defining Relative clause
Professor Potter, who teaches Eng 10, is an excellent lecturer. Professor Potter, whom I met yesterday, teaches Eng 101.
We took some children on a picnic. The children who wanted to play soccer, ran to an open field as soon as we arrived at the park (The use of commas, means that all of the children wanted to play soccer and all of the children ran to an open field. the adjectival clause is used only to give additional information about the children.)