Communication Security is securing emails, instant messaging, telephone calls and text messages to an extent that no third parties be it Hackers, Criminal Organizations, Your ISP, Government or even the Service Providers themselves can Intercept or Spy on them.
Communication Securtiy provides means by which people can share information with varying degrees of certainty that third parties cannot intercept what was said. Other than spoken face-to-face communication with no possible eavesdropper, it is probably safe to say that no communication is guaranteed secure in this sense, although practical obstacles such as legislation, resources, technical issues (interception and encryption), and the sheer volume of communication serve to limit surveillance. Secure communication is when two entities are communicating and do not want a third party to listen in. For that they need to communicate in a way not susceptible to eavesdropping or interception.