if a couple is to lack communication. does thatean that lack in trust. more do they really. care about the other?

To me if they really cared then they would communicate with each other no matter what, when or where. Never assume the other knows how you feel or think tell them now. To me trust is earned by actions so don’t rush into a serious relationship without it .

Communication is THE most important thing in a relationship. unfortunately no one has learnt to do this right, we've all been taught to be nice, polite, respectful, blabla. Very nice, but doesn't help a relationship where you have to dare to be open and tell how you truly feel.
What most do is assume the other will know how we feel, think, and what we need. The other will do the same, et voila, the first cracks in the relationship appear.

It's about healthy communication, which means not blaming the other for how you feel, but simply telling how you feel and leaving the other out of it. That way you don't get action-reaction but true communication.
And yes, that will help trust to grow.

Communication and learning to communicate in a relationship generally facilitates the growth of trust and caring. Communication is ultimately information sharing and understanding.

A lack of communication doesn't inherently mean there is a lack of trust or caring, especially in an absolute sense, it may mean there just isn't enough there to support the relationship or relationship roles/expectations.

Kinda depends on why there is a lack of communication.
Are they actively working against communicating? Are there just "natural" or more organic reasons related to personality or compatibility which either inhibit or get in the way of communication, like personal communication abilities, e.g. one person relies on verbal, the other more dependent on non verbal? Are there external things/situations getting in the way?

I mean there's a huge difference between:
"They refuse to talk to me."
"Every time I confront them with conflict, they run away, or it escalates out of control!"
"Our cultures are totally different, they do (x) but to me that means (y) and they/I can't understand that mindset."

Does the couple lack communication and it's a recent thing?
Like communication was great in the beginning but it's changed?
Just the expectations of communication, like desired growth to something that isn't being experienced?
Or was there always a lack of communication? Why is the lack important now but wasn't then?

Other than that, or maybe tldr is a lack of communication does not inherently mean there is a lack of trust or caring.

Hmm.

Be VERY VERY careful with your thinking about this.

One of the most dangerous and often destructive things I see people in relationships do to each other again and again, is when they contrast something they are experiencing with their mate, and compare it to some fantasy they have about life....and then conclude some oversimplified thing like "if he/she doesn't try harder to talk to me, it means they don't really love me after all."

Life and people are VASTLY more complicated than that.

ESPECIALLY when it comes to communication.

There are many reasons why a person can be poor at expressing their feelings, which have nothing at all to do with their not feeling deeply. Even when someone is afraid to communicate, it doesn't necessarily mean they don't trust the other person. It's much more common, that they don't trust their own ability to say what they really mean, clearly enough.

No it doesn't necessarily lack trust or mean they don't care about each other.

Some people just don't communicate well with each other.

Probably many couples out there like that.

Doesn't make a real good relationship in a marriage especially.

Not necessarily. Sometimes when there is little communication, people can interpret that as everything is good. Being raised in two different households plays a factor when it comes to communication, independent of trust issues. Perhaps they're avoiding discussing problems; doesn't mean they don't trust each other. Maybe they're scared of the outcome of the conversation.