Meaning:
“大” means “big,” and “白” means “white.” This is the Chinese nickname for Baymax, a character of Disney’s 2014 animated feature film “Big Hero 6.” He is an inflatable computerized robot covered in white, and serves as a personal healthcare companion. Selfless and caring, Baymax becomes one of the Big Hero 6 team after some deft reprogramming that gives him superpowers. Chinese netizens use it as a nickname for frontliners who are fighting the COVID-19 pandemic, because they wear white protective coveralls on the job and they work selflessly to protect the safety of the public.
Example:
A: 你今天验核酸了吗？
Nǐ jīntiān yàn hésuān le ma？
Did you have your nucleic acid test done today?
B: 还没，我们小区的检测点还没看到“大白”，今天大概要晚点开始。
Hái méi ，wǒmen xiǎoqū de jiǎncèdiǎn hái méi kàndào “dàbái ”，jīntiān dàgài yào wǎn diǎn kāishǐ。
Not yet. I haven’t seen the frontliners in white protective coveralls at the test site in our housing estate today. I guess testing will start a bit later.