abstract A class modifier that specifies that the class must be derived-from to be instantiated. as A binary operator type that casts the left operand to the type specified by the right operand and that returns null rather than throwing an exception if the cast fails. base A variable with the same meaning as this, except that it accesses a baseclass implementation of a member. bool A logical datatype that can be true or false. break A jump statement that exits a loop or switch statement block. byte A one-byte, unsigned integral data type. case A selection statement that defines a particular choice in a switch statement. catch The part of a try statement that catches exceptions of a specific type defined in the catch clause. char A two-byte, Unicode character data type. checked A statement or operator that enforces arithmetic bounds checking on an expression or statement block.