The underlined words are a(n) appositive phrase.
absolute phrase.
restrictive clause.
independent clause.

My father, an electrical engineer, patiently explained the confusing material in my science textbook.

appositive phrase.

Explanation:

An appositive phrase is a noun or a noun phrase that provides another name for a previously mentioned noun. The additional name given to that noun provides a clearer meaning or more information that enhances our understanding of the sentence. The phrase, "an electrical engineer", provides more information about the noun "father", thus helping us to understand why the student's father was qualified to answer the question in the science textbook.