This question is more suited to r/politicalscience or a similar subreddit, because it is closely related to the comparison of the activities of the polity against various political and legal concepts.

Despite its prevalence since the second half of the 20th century, the term 'terrorism' is very vague and is often applied to various actions and ideologies that are more or less invariably tied to a small groups commencing acts of violence and thus became inseparable from such image to the point that the other form of modern terrorism, namely the 'state terrorism' is much less popular, even though it is where the term originates, as it was first used to denote the supporters of the anti-royalist faction during the second stage of French Revolution. From that standpoint, Mongols (whether the Golden Horde or any khanate it later divided into) or any other large polity cannot be defined as 'terrorists' because they are, well, large polities and not small groups, and their acts of violence against other people fit the definition of war rather than terrorism.

There is also another facet of the terrorist actions that according to some definitions plays the pivotal role as it makes the difference between the terrorism and rebellion, insurgency or war. Namely, it is the observation that acts definable as terrorism are conducted to further some goals (by intimidating other party to take actions desirable by the terrorists) which goals are pursued by the the people otherwise unable to achieve these goals directly, through political or military action. The Golden Horde, khanates or Kipchak-Cuman confederation had all the means to achieve their goals through regular military conflicts and thus their actions are considered to be directly militant. Conversely, severe punishment of criminals up to and including qualified death penalty has been often openly defined as a deterrent (what boils down to the intimidation of prospective criminals), but are not considered terrorist actions, because they are applied by the party that possesses the actual authority and means to uphold the law.

At the peak of the power, Golden Horde was using what could have been considered 'terror tactics' by razing large cities during the conquest of Kievan Rus and Persia but this was pretty regular modus operandi of the Mongols who often resorted to the dismantling of the city defenses to ensure that it won't be able to efficiently rebel against their rule (this was, of course, not unique to them, as evidenced by the destruction of Sarmizegetusa in 106 during Roman-Dacian wars) as well as the well-known tactics during a large-scale conquest, especially in the politically fragmented areas, to prevent resistance mounting in a conquered area. Please note that the similar actions taken by German Army and SS troops during the Second World War are considered war crimes rather than acts of terror, even though some of them were conducted precisely to enforce compliance among the conquered populace. It should be also noted that the razing of cities or massacres of non-combatants, although relatively rare, were not something unheard of, both in Middle Ages and modern times with the best known examples being the razing of Jerusalem in 1244, uprising in Palermo of 1281 (Sicilian Vespers) or Sack of Magdeburg in 1631.

Summing it up, the actions of Mongols were a part of military conquests and bear similarities to what amounts to war crimes in modern times, although they can't really be categorized so in historical context, as no such trans-cultural legal provisions existed back in the day, not to mention that imposing modern perspective on historical events is usually considered bad practice.