The Boolean datatype has two values - True and False.
if ( (input.Terms and conditions== "false") )
alert "Please agree to the terms and conditions";
cancel submit ;
Functions that operate on boolean expressions are classified as Logical functions. They include functions for returing "true" if value/expression is empty, date or a string etc. Refer the topic Built-in-functions - Logical Functions for the complete list of Logical functions.