What does "all day" mean?

For the period of an entire day, or at least during all the daytime of a day.

All day

adv

adv ·Rare ·Advanced level

Adverb

1
For the period of an entire day, or at least during all the daytime of a day. not-comparable
"There hasn't been a breath of air all day."
2
Easily; handily; in spades; by far. figuratively, not-comparable
"Well, for twenty quid we're having it — it's worth that all day long."

"There hasn't been a breath of air all day."