What does Linux less -w or -W option do?

Less -w or –hilite-unread option temporarily highlights the first “new” line after a forward movement of a full page. The first “new” line is the line immediately following the line previously at the bottom of the screen.  Also highlights the target line after a g or p command. The highlight is removed at the next command which causes movement. The entire line is highlighted, unless the -J option is in effect, in which case only the status column is highlighted.

Less -W or –HILITE-UNREAD option is similar to -w option, but temporarily highlights the first new line after any forward movement command larger than one line.