Don't be fooled by the name: a liqueur and a liquor are two distinctly different tipples. Whereas both are fermented and distilled, liqueurs have been sweetened and flavored with fruits, herbs, spices, or a combination of the three.
They are also generally lower proof than liquors, often falling somewhere between 30 and 70 proof (15% to 35% alcohol by volume). Of course, there are some exceptions and some liqueurs can go much higher in alcohol content. The only major defining trait is that all liqueurs have been sweetened in addition to having been flavored.
Historically, liqueur referred only to those spirits that were sweetened and flavored with fruits whereas cordial referred only to those that were flavored with herbs. Today those distinctions have been largely ignored and you will often see the terms being used interchangably. Check this section for some of the familiar staples like amarettos, triple secs (and other orange liqueurs like Cointreau and Grand Marnier), pastis, and sambucas as well as great classics like absinthes, amaros, and limoncellos. This is also the place to look for any and all crème liqueurs (not be confused with the cream liqueurs) like crème de cacao, crème de menthe, and crème de cassis. These do not contain any dairy cream; rather, they have been sweetened to a near-syrupy consistency, so the crème refers to this thickness.
There is a whole world of unique and often surprising cordials and liqueurs to explore and add into your repertoire. From sweet to bitter, delicate to bold and brash, cordials and liqueurs can elevate some of your favorite cocktails or steer you towards new and exciting directions when deciding what to mix up for your next gathering.