Answer:
yes , you an compress all states of matter except solids. gases are easier to compress. if u put your hands out and press down but dont clap, that is considered compressing gas
add. Actually solids may be compressed in some circumstances. e.g. This was the consideration that gives us the atomic bomb - the solids are compressed (by explosive devices usually) - and this allows the density of neutrons to increase beyond the 'critical point' the self-sustaining reaction.
Less terrifyingly, graphite may be compressed in an 'anvil machine', to convert it into diamond.