Yes,panel lines~its there on our kits but we often ignore it.Panel lines if done correctly will made the kit you're building more appealing,it gives others a "wow factor" and your peers knows you're taking care of your kits to that very detail.I'm not fond of panel lining,its a messy job but yet,its a must.here's some pics of the difference between panel lined piece and a bare "stock" piece.
This is the basic things you need,gundam markers and an eraser.
Bare piece.
Panel lined.
Closer look.
There's some other methods for panel lining,some used the gundam pencil lead and the "pro" way,using enamel. =)