A lodge is a permanent building, usually set on a ridge or escarpment with a long view over the plains. You get a solid room with a private bathroom, reliable hot water, electricity through the night, a restaurant, a bar and very often a swimming pool looking out over a waterhole.
Lodges suit travellers who want the wilderness outside the window rather than through the canvas. They are the easiest option in the wet season, the most comfortable for anyone with mobility concerns, and the most reassuring for a first safari or for families with small children.
The better lodges in Tanzania are built into their setting rather than on top of it — local stone, thatch and timber, water heated by solar, and rooms angled so that every one of them faces the view. Wildlife still walks through: buffalo graze the lawns at Ngorongoro and elephants use the Serengeti waterholes, so you are escorted to your room after dark.