Most acronyms are formed from the first or first few letters of a series of words and are usually pronounced as words. If an acronym contains six or more letters, capitalise the initial letter and lowercase the others.
Erasmus (European Community Action Scheme for the Mobility of University Students)
Europol (European Police Office)
NATO (North Atlantic Treaty Organization)
Initialisms are usually formed from just the first letters of a series of words. Generally speaking, write them following the upper- or lower-case pattern of the full term. When the full term is in lower case, they are usually separated by points.
MBA (Master of Business Administration)
e.g. (exempli gratia)
i.e. (id est)
Note, however, that the abbreviation plc (public limited company) is always written in lower case but without points.
In higher education, some initialisms representing degree studies combine upper and lower case and do not take points.
BSc (Bachelor of Science)
PhD (philosophiae doctor)
Note, too, that an initialism may take capital letters even when the full term does not.
«Forming acronyms and initialisms» [en línia]. A: Criteris de la Universitat de Barcelona (CUB). Style Guide. Barcelona: Universitat de Barcelona. Serveis Lingüístics. <https://www.ub.edu/cub/criteri.php?id=2358> [consulta: 6 maig 2021].