Yeah, it's been commonly used when the object (in the grammatical sense) would typically have a gender but it is unspecified. In fact, it's so common native English speakers don't even notice they're doing it. (Which produces a steady stream of unintentional humor from those pretending it isn't a thing.) The usage as a sign of respect for specific non-binary and other gender non-confirming people is more modern (2009 is apparently the first recorded example). Although to a great extent, it doesn't matter. Language evolves over time and dictionary definitions necessarily trail usage.
The wikipedia article is quite detailed and will probably supply more information that anyone particularly wanted. https://en.wikipedia.org/wiki/Singular_they
