To me, communication is a much overlooked part of engineering. As I've advised my children (both engineers), no matter how good your ideas and solutions are, you need to be able to explain them clearly and "sell" them to others, so they will implement them.
Also be genuinely open to other's ideas (acting interested), and be able to explain why you agree or disagree without making it personal. If you agree with part of their ideas, work them into yours and show you are a team player. This makes it easier for them to contribute in the future, without worrying about being ignored or ridiculed.
So I guess that, besides being clear and correct, communication means establishing mutual respect.
They might be asked to submit information to people of non technical or scientific backgrounds, whose knowledge level in the subject may be null, thus a problem here arises of how to explain the phenomena in a way that gets their intended messege across effectively and does not leave the audience feeling bored, and cheated.
Engineering problems are rarely presented with complete information in writing. Conversion of such a problem to an appropriate form of media could be another issue, Communication skills can be taught. There are also always time and monetary constraints when trying to generate new information or present/convert it in a form that is different.
At one time I was asked regularly to give a "What do Engineers do?" speech at a local university for a Department-head friend. At the end of the presentation I would show a slide indicating all the skills an Engineer needs. Analytical problem solving, design, blah blah, typical Engineer stuff. I also added soft skills of communication (written & verbal), diplomacy, marketing, salesmanship, influencing skills, yadda yadda yadda.
A circle would fly out to capture the hard stuff and I would say "THIS is what you need to keep your job every day."
Another circle would fly out and capture the soft stuff. I told the students "THIS is what you need to grow your career."
Invariably, the majority of the students became depressed and demotivated.