You can say that a group of lettersis the/an abbreviation forsomething.
DST is the abbreviation for daylight saving time.
You can also say that a group of lettersstands forsomething oris short forsomething.
GPS stands for "Global Positioning System".
Jo is short for Josephine.
You can also say that a word or phraseis abbreviated tosomething oris shortened tosomething. These two uses are less common.
The word "immunoglobulin" is often abbreviated to "Ig".
The word "propeller" is often shortened to "prop".