In Hawaii, one meaning of the word ‘pu’u’ is ‘a protuberance of some kind.’ This can be anything from a pimple to a hill, but ‘hill’ is the most common usage I encounter, as a general reference or in place names.
Pu’u O’o is the cinder cone that is home to the vent on Kilauea Volcano that was active from 1983 until earlier this year. Pu’u Wa’awa’a is an old cinder cone that is now managed by the Division of Forestry & Wildlife. A common thread is that, in Hawaii, a hill is a cinder cone because all of Hawaii is volcanic and the landscape is liberally dotted with cinder cones.
The top photo shows Mauna Kea and the large array of pu’us on its southern slopes. In the foreground is Pu’u Huluhulu, which means hairy hill. There’s a trail to the top of this pu’u which offers good views of Mauna Kea and Mauna Loa.
The bottom photo shows grassed over pu’us in Pōhakuloa Training Area, which is a military base located in the region between Mauna Loa, Mauna Kea and Hualālai volcanoes.
On the Big Island, several pu’us are accessible to hikers, usually with a trail curving up to the top and then around the rim of the pu’u. Even if the pu’u isn’t that high, it invariably stands out from its surroundings and offers good views.