“spirits” and “liquor” are the same thing: a hard (the hardest) alcohol product made by distillation and has around 40% alcohol by volume (ABV), possibly flavored but always unsweetened.
Of course, the term “spirit” (aka liquor) doesn’t refer to everything you see in a liquor store besides wine and beer. For instance, you may also see bottles with names like Grand Marnier, Amaretto, or Angostura bitters. These are all part of the colorful, intoxicating extended spirits family, but they’re not quite spirits (because they’ve had things like sugar, herbs, and spices added to them and tend to have lower ABVs).
So how can you spot a spirit/liquor? These days, all spirits bottles have to be labelled with some pretty specific information: the brand name; the kind of spirit in the bottle (e.g. vodka, gin, tequila, rum and whisky), though you may also see things like mezcal, pisco and cachaça); any further required details regarding the spirit, for instance the age of the whiskey if it’s under four years; the alcohol by volume (or ABV), which must be written as a percentage but will often also be labelled as “Proof”; the country of origin.