What does "third degree" mean?

Intensive questioning or rough treatment used to obtain information or a confession, as in The detectives gave her the third degree, or Jim gave her the third degree when she came home so late. This term comes from freemasonry, where a candidate receives the third or highest degree, that of master mason, upon passing an intensive test. Dating from the 1770s, the phrase was transferred to other kinds of interrogation in the late 1800s.