Question

What does frequency mean in science

Answer 1

A rate at which a cycle or phenomenon is repeated.

Answer 2

There's nothing mysterious about it at all. "Frequency" simply means
"often-ness" ... how often or how frequently something happens.

-- The frequency of traditional meals is 3 per day.
-- The frequency of an equinox is 2 per year.
-- The frequency of my sleeping really late is 1 per week.
-- The frequency of my intense desire to sleep late is 30 per month.
etc.

-- The standard unit of frequency in the SI system is "per second".
The special name for that unit is "Hertz". (Hz)