Like in any other language, Spanish has words that are used only in the plural form. This is referred to as Pluralia tantum (from Latin). In dictionaries, it is abbreviated as plt
For example: gafas, f plt
Here are some of the commonly used words that exist only in the plural form:
Nouns and things:
las gafas – glasses;
las vacaciones – vacation, time off;
(en) las afueras – outskirts, surroundings;
los víveres – food, supplies, provisions;
las andas – stretcher;
los celos – jealousy
las tinieblas – darkness; ignorance;
los bolos – bowling pins;
Institutions:
las Cortes – The Spanish Parliament;
Correos – Postal Service
Bomberos – Fire Department
Geographic names:
Los Estados Unidos – USA
Los Pirineos – Pyrenees
Los Andes – Andes