message as in a communication (usually brief) that is written or spoken or signaled
"he sent a three-word message"
message as in what a communication that is about something is about
contentsatisfied or showing satisfaction with things as they are; satisfy in a limited way; make content; (usually plural) everything that is included in a collection and that is held or included in something; what a communication that is about something is about ; the proportion of a substance that is contained in a mixture or alloy etc. ; the amount that can be contained; the sum or range of what has been perceived, discovered, or learned ; the state of being contented with your situation in life; something (a person or object or scene) selected by an artist or photographer for graphic representation
subject matter what a communication that is about something is about
substance the real physical matter of which a person or thing consists; the choicest or most essential or most vital part of some idea or experience; the idea that is intended; material of a particular kind or constitution; considerable capital (wealth or income); what a communication that is about something is about ; the property of holding together and retaining its shape; a particular kind or species of matter with uniform properties