Generally, each of the various tension "versions" of a particular string model are manufactured in pretty much the same way, but with more or fewer windings to change the mass, and therefore the tension. Yeah, that's what we need - more confusion.
Though, some manufacturers designate them differently Corelli's 370 Strings come in "Medium," "Forte (heavy)," and "TX/Extra Forte (extra heavy)," while Eurosonics come in "Medium," "Light," and "Ultra Light." And, just to be different, some string makers designate their medium strings as "Orchestral" gauge. Those that offer additional string tensions usually designate the "standard" gauge as "Medium" (or "Mittel" if they're certain European brands), and then a "Light" ("Weich" or "Dolce") and/or "Heavy" ("Stark" or "Forte") gauge. Specifically, the strings have more or less mass, to require a few pounds more or less tension to create the specific pitch desired, which makes the strings feel "tighter" or "looser."
What's the diff? Simply, light strings have slightly less tension than mediums, and heavy strings have slightly more tension.
Some strings come in only one weight, but quite a few have multiple tension options. To start off with a generalization, most players use mediums, in my experience selling strings.