Short answers, pulled from the story.
The 10th century Cleopatra Glossaries define the Latin word orcus as an Old English term meaning goblin, spectre, or hell-devil. Thomas Wright noted that Orcus was the name for Pluto, the god of the infernal regions. Tolkien adopted this specific term from these old attestations purely for phonetic suitability.
The first edition of The Hobbit published in 1937 used the term goblin only once. Orc appeared ubiquitously later in The Lord of the Rings. J.R.R. Tolkien wrote that his orcs were influenced by the goblins in George MacDonald's 1872 novel The Princess and the Goblin.
J.R.R. Tolkien stated in a letter dated the 21st of October 1963 to Mrs. Munsby that there must have been orc-women. This admission contradicted earlier suggestions that they were merely beasts of humanized shape. Shippey argues these creatures served as infantry for an old war ready to be slaughtered without compunction.
Most orcs avoid daylight until new breeds emerged from Mordor attacking Osgiliath by the late Third Age. These Uruk-hai were larger, more powerful, and no longer afraid of sunlight. They garrisoned Isengard serving Saruman while eating meat including the flesh of Men.
Dungeons & Dragons implemented orcs as multi-tribed hostile bestial humanoids with muscular frames and large canine teeth. The original edition from 1974 gave them pig-headed looks rather than Tolkien's pug-nose description. Later versions shifted from bald-headed to hairy and eventually gray-skinned in the third version.