What is it called when you shorten a word to only its important letters?

ex.

package --> pkg
theorem --> thm
proof --> pf
function --> fn
config --> cfg (this is a bit uncommon)
attribute --> attr

Example sentence:

This process is called _____.

Solution 1:

They are called abbreviations:

abbreviation:

a shortened or contracted form of a word or phrase, used to represent the whole, as Dr. for Doctor, U.S. for United States, lb. for pound.

(Dictionary.com)

Solution 2:

Those words are foreshortened, e.g.

Morse code abbreviations are used to speed up Morse communications by foreshortening textual words and phrases. Morse abbreviations are short forms representing normal textual words and phrases formed from some (fewer) characters borrowed from the words or phrases being abbreviated. [...] e.g. ctl for control - https://en.m.wikipedia.org/wiki/Morse_code_abbreviations

And the definition from Princeton's WordNet:

foreshortened. abridge, foreshorten, abbreviate, shorten, cut, contract, reduce(verb) reduce in scope while retaining essential elements "The manuscript must be shortened" - https://www.definitions.net/definition/foreshorten