Masking is when someone understates or selectively shows their true opinions. I wrote an article on masking and how to get others to maintain dialogue when masking occurs, check it out here.
Examples of masking:
From the book Crucial Conversations, there are 2 key strategies people follow under tense situations:
Flight or Fight — or in their words, Violence or Silence.
Masking, is a Silence strategy people follow. It’s used mainly by people who move towards Silence (or Flight) in tense situations.
When people feel unsafe, they tend to start to use strategies like masking to avoid giving all information as to avoid potential problems.