does it have to be spoken?
can it be shown?
how?

Hard to find, easy to loose, happiness and tears in between

The same as the dictionary or medical/psychological definitions, a general or technical definition when discussing it with people with whom I have no relationship or direct interactive experience.

Otherwise, the definition becomes more subjective when there is context and understanding based on shared information, commonalities, culture, communication, etc., the things that make up a relationship.

I do know a lot of people like to try and subjectively predefine the word/concept, then discuss it with others (like potential dates or on forums) trying to cherry pick commonalities. All to try and build a relationship and emotional bonding on flawed foundations.
As opposed to try and build a relationship engendering emotional bonding, and then try to adequately express/communicate what they are actually feeling.


"Have" to?
Hypothetically/theoretically, no. Mute people find a way to express their emotions/feelings.
Practically speaking, generally yes (outside of mutes), assuming you want a relationship to continue.


Sure. It "can."


Through effective communication. Words and actions and situations which are subjective/relevant to the individuals involved.


Are you "really" asking or looking for something more like "is there a compartmentalized absolute information packet someone can label as 'love' which they can present to absolutely anyone, anywhere, at anytime, and the recipient will be triggered into feeling and/or absolutely understanding and/or accepting as absolutely true the emotional state/understanding/feeling of the person expressing or 'defining' love?"
Then, no.

Love makes and can unmake

Love is the beginning and the end,
and everything in between.

Well well we agree on something