Hi,
While the gentlemen above are correct how lines can easily be hidden, you may rather be interested in softening those edges instead, if they are on a terrain.
To do this, right click on the terrain component and select soften edges. A dialogue will pop up where you cn check "soften coplanar edges" and use the slider to soften what you want.
You can also soften individual edges (in edit mode) using the Ctrl+Erases tool.
Softening a terrain would probably give you better visual results than only hiding edges because by hiding them the surface will stilll ermain "broken".