From Wikipedia: "The U.S. Code of Federal Regulations defines terrorism as the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives". Given his proclamations as he killed 49 innocent people, the Orlando shooter certainly fits the definition of a terrorist. Unfortunately, his actions do not fit the narrative for the liberal political and media elites so they attempted to brand it as "gun violence" to further the anti-gun agenda or he is a self loathing gay man and therefore a victim of a society that refused to accept him. This is not an isolated incident either. Remember when the Obama administration tried to re-brand the Fort Hood terrorist attack as "workplace violence"? Luckily these re-branding attempts have gotten little traction with the American public who are increasingly aware that ISIS is a terrorist organization that is continually mounting assaults on the innocent citizenry of western and middle eastern countries of all faiths (including Islam) in the name of Islam. And the reason that the term terrorist has become commonplace and often associated with Islam (e.g. Islamic Terrorists) can be found right here in Wikipedia.
To try to say that the Orlando shooter should not be branded as a terrorist because the shooters in Sandy Hook or the Aurora Theater were not branded as terrorists is an attempt to create a false equivalency. From what we know about Sandy Hook and Aurora, these heinous acts were committed by individuals with no stated political or social agenda. If they did have one, then they should/would have been branded as terrorists.
And by the way... any intelligent person will tell you that not all terrorist acts are perpetrated in the name of Islam. Take a look at the Irish Republican Army for example. They are a terrorist group and were considered as one by the US government until 1997 when they adhered to a cease fire. Of course any group that kills 1800+ people in the name of a political agenda should always be considered a terrorist group even if they stop committing terrorist acts.