What is the example and a non-example of compression and what are characteristics of it?

What's a non-example? Is it a situation which definitely excludes any of something (in this case compression) ? Almost everything we encounter in our daily lives will be under some compression, if due only to atmospheric pressure or self weight. So we need to go for example inside the walls of a vacuum flask or other vacuum vessel to get to the residual gas which has virtually no compression.