What does instantaneous mean?

occurring or done in an instant or instantly.

Explanation:

or

existing or measured at a particular instant.

u probably want the first one

Something that is done in a instant, like quickly or out of the ordinary.

Explanation:

The dictionary definition is ... (Adjective) "occurring or done in an instant or instantly."

an example is ... "modern methods of instantaneous communication"

If you are refering to science it is ... "existing or measured at a particular instant."