Final answer:
The term "frat" is a colloquial abbreviation for "fraternity" and is commonly used, but its customary usage can depend on context and preferences. Some may prefer "fraternity" for its formality and respect.
Step-by-step explanation:
The term "frat" is indeed a colloquial abbreviation for "fraternity", and it is commonly used, especially within the context of college campus life.
However, saying whether it is customary to use "frat" instead of "fraternity" can depend on various factors, including the formality of the context and personal or organizational preferences.
Some members of Greek life organizations might prefer the term "fraternity" as it carries a more formal and respectful connotation, while others might use "frat" in casual conversation. Ultimately, it is important to be aware of and respect the preferences of the individuals and organizations you are interacting with.