What does the term normally open mean

Relays and momentary switches have a state that they are in normally, or in a relaxed state, as in not energized. The contacts of these switches or relays can be either open (off) or closed (on).

Normally open describes the state of a set of contacts in a momentary switch (manual switch that springs back to "open" state when released), the circuit is open until the switch is pushed.

A set of "dry" contacts, aka a form 'C' contact, aka SPDT, has a common pole and one normally open and one normally closed contact, allowing the user to arrange the state of the circuit in the manner required.

In the linked illustration, the spiral line with the bar next to it represents a coil that changes the state of the contacts when energized.

"normally" in this instance means "de-energized"

DPDT is two sets of contacts controlled by the same coil
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