A label is a symbol that represents an address. A label's scope depends on whether the label is local or non-local.
The syntax of a label is:
label ::= local_label [ : ] | non-local_label[ : ]
The default settings are that each label ends with a colon (:), a label can begin in any column. However, if you port existing code that does not follow this convention, you should clear the Labels must end with ':' checkbox of the Assembler settings. After you clear the checkbox, you may use labels that do not end with colons, but such labels must begin in column 1.