Something that is symmetrical along a line. Like you could fold it in half and it would be the same. Like a rorschach inkblot. A butterfly. A person.
The other kind of symmetry is radial symmetry, which is symmetrical from a point. Like a starfish. I think things that are radially symmetrical are always also laterally symmetrical, but there could be some weird exception to that that I can't think of.
Bi-Lateral.
Yes. Pigs, like all vertebrates, have bilateral symmetry. This means they have symmetry across one plane (known as the sagittal plane, and directly down the centre of their body), which means one side of their body approximately mirrors the other side.
The lungs are directly lateral to the mediastinum.
Arial symmetry
The ulna and radius bones lie lateral to the wrist.