An ABL expression is a combination of one or more terms and operators that evaluate to a single value of a specific data type. An expression can include constants, variable names, database field names, or other expressions.

ABL has a set of operators for working with numeric, string, date, and logical data. The data type of the data must be compatible with the operator. One very useful operator is the concatenation operator (+), used to join two character strings or expressions: 
FOR EACH Customer:
  DISPLAY Customer.Name Customer.City + ", " + Customer.State FORMAT "X(20)".
END.
More information on the ABL operators can be found in the ABL Syntax Reference.