what is % in a Abap code?

i have a report which uses % everywhere.

No idea what that means?

part of the code is like this..

DATA %data_selected(1).

DATA %glframe(1) VALUE 'X' .

DATA %uflag(1).

DATA %ustflag(1).

SELECTION-SCREEN: BEGIN OF LINE.

PARAMETERS: %alv RADIOBUTTON GROUP func USER-COMMAND outbut

DEFAULT 'X' .

SELECTION-SCREEN: COMMENT 4(26) text-f72 FOR FIELD %alv.

PARAMETERS: %alvl TYPE slis_vari.

SELECTION-SCREEN: PUSHBUTTON 72(4) pb%exco USER-COMMAND expcol.

SELECTION-SCREEN: END OF LINE.