In plain words
What treatment-resistant depression means
Depression is a common health condition in which low mood, loss of interest and other symptoms are more intense than everyday sadness, last two weeks or more and get in the way of daily life. It is usually treated with psychological therapy, medication, or both, and it can take time and some adjustment to find what helps.
When depression has not improved enough after treatments have been given a fair trial, doctors sometimes describe it as treatment-resistant or difficult-to-treat depression. There is no single agreed definition, and the term describes how treatment has gone so far rather than anything about you.
This is general information, not a diagnosis. Source: Healthdirect: Depression.