Regardless has 5 different meanings across 3 categories:
(usually followed by `of') without due thought or consideration
"careless of the consequences"
"crushing the blooms with regardless tread"
Having no regard; heedless; careless.
"The reckless driver sped through the red light regardless of the flashing police sirens behind him."
In plain English: Regardless means without caring about something else.
"The plan remained regardless of what happened."
Usage: Use regardless only as an adverb to mean without considering consequences or rules, not as an adjective describing someone who is careless. Do not confuse it with the noun disregard when you need a word that functions grammatically before another noun.
in spite of everything; without regard to drawbacks
"he carried on regardless of the difficulties"
Without attention to warnings or indications of bad consequences.
"He decided to drive through the heavy storm regardless of the flashing warning signs on the highway."
In plain English: Regardless means doing something without worrying about whether other conditions are true or not.
"He went for a walk regardless of the rain."
Synonym of regardless of; paying no attention to
"She decided to go for a run regardless of the heavy rain falling outside."
The word regardless comes from combining the verb regard with the suffix -less to mean "without paying attention." It entered English as a straightforward formation describing someone who does not consider something important.