Which of the following is NOT an entitlement? A. Social Security B. Medicare C. Worker's Compensation D. Head Start E. Unemployment which...

An entitlement program, in American terminology, is one where the government sets criteria for participation and then everyone who meets the criteria is automatically given the benefit that the program calls for.  The Congress does not have to vote to appropriate money for entitlement programs every year.  Instead, the government is obligated to pay for those programs.

With other kinds of programs, the Congress has to vote every year (or every so often) to fund the program.  Not everyone who qualifies for the program necessarily gets the benefit.  Instead, people get to use the program until money runs out.  This limits the reach of these programs.

Of the programs that you list here, all are entitlements except for Head Start.  Head Start has to be funded by Congressional vote.  Not every child who qualifies actually gets to use this program.