DelVar is a basic control used to delete a variable from the calculator. This increases the memory available for other variables, but the deleted variable cannot have its value recalled.
Storing a value to a variable will undelete the variable.
:DelVar var1, var2[, var3, ...]
This deletes multiple variables in a single command.
:100→X :DelVar X
In this case, the integer 100 is stored inside the variable X. The next line uses DelVar to delete the variable X.