My grandmother was a german teenager of jewish descent during the war, which made her, her sister and her father a target of persecution by the nazis. She and her sister somehow survived the entirety of the war hiding in Berlin, while his father wasn't as lucky, getting caught at some point and sent to a concentration camp. Fortunately, he did survive, and the three of them were able to reunite after everything was over.
This question popped up in my mind the other day, when me and my father were talking about my grandma (her mother, who passed away more than a decade ago) and the hell she must have gone through during WWII. When I referred to her as a holocaust survivor, my father was quick to correct me saying that the label wasn't adequate, as she had never gotten imprisoned at a camp. I argued saying that really wasn't important, since she was the victim of ethnic persecution, probably facing hardships and atrocities I could never begin to imagine. He did comply to that, but still insisted that "Holocaust survivor" wouldn't be the correct term for her experience, technically speaking.
Thus, I wanted to hear some other opinions on the matter, as human experiences throughout historical events of this magnitude tend to be incredibly complex and hard to categorize in labels.
In a way, this is a subjective question and opinions will vary. I can see how your father and others might want to reserve a special category for those in the camps themselves. However, we can look at what memorial institutions consider to be a Holocaust survivor, and that will point us to a more broad definition that has been used in practice for decades.
For example, the United States Holocaust Memorial Museum has a Survivors Registry division that collects and archives survivor information, stories, and interviews. According to its definition of "Who is a survivor?":
Holocaust survivors are Jews who experienced the persecution and survived the mass murder that was carried out by the Nazis and their collaborators between 1933 and 1945. This included those who were in concentration camps, killing centers, ghettos, and prisons, as well as refugees or those in hiding. Holocaust survivors also include people who did not self-identify as Jewish, but were categorized as such by the perpetrators.
Roma and Sinti, Poles and other Slavic peoples, Soviet prisoners of war, persons with disabilities, political prisoners, trade union leaders, “subversive” artists, those Catholic and Lutheran clergy who were seen as opponents of the regime, resisters, Jehovah’s Witnesses, male homosexuals, and criminal offenders, among others were also victims of Nazi persecution.
So that definition overtly includes "refugees or those in hiding," not just those in the camps. Within the USHMM oral history collection, there are a lot with survivors who were not in camps -- which makes sense, considering the death rates. From my memory of interviews in the collection, there are stories of hiding in barns, escaping to other countries ahead of the Nazis, living in the woods with partisans, fleeing to Italy and being held on a sort of prison island... all kinds of stories of persecution and loss that go beyond the camps alone.
Another institution, the Museum of Tolerance, features live survivor talks. A quick check of their current schedule shows several who survived the war in hiding.
The Illinois Holocaust Museum features a very cool "interactive hologram" interview with a survivor. (They filmed a bunch of different conversations and anecdotes, and turned it into a hologram. You can ask the hologram a question and it will answer from its video files. It's neat!) At least one of those is a survivor who was a child in hiding.
So with those examples, we can see that the institutions of memory are pretty united on the broader view of survivorship, rather than the more limited one your father proposed. In my experience it's the consensus view of the historical community, which is generally not interested in debating "who had it worst?" and reserving labels for some and not others. It's better to take each person's story on its own terms, and understand that there were many different persecutions and acts of terror that added up to the big thing we call The Holocaust. And so there can be many different types of survivors.