Elderwood is a block of Wood with umber bark and pale brown wooden core taken from an Elderwood-tree.
Pine-like Elderwood-trees with dark evergreen Elderwood Leaves can be found in Mountains, snow-covered Tundra and (sometimes snowy) Taiga biomes. Special giant thick Elderwood-trees can rarely be spotted in Savannahs too, they look like foliage trees there and their trunk is hollow.
Since R14 Elderwood-trees can have one thick foliage tree - like shape and two basic pinetree-like shapes - a slender one, and a bit taller one with 2x2 blocks wide trunks - the larger specimen can often be seen in Tundras.
Before R14 some Elderwood-trees could grow really tall like giant sequoias / redwoods and looked like foliage trees with trunks up to 10x10 blocks wide at their base and many branches (different from the current Savannah-type with a compact leaf canopy).
Nowadays in cold areas Elderwood-trees can be snow-covered and/or even have snowy leaves whitened by frost - however if you harvest those leaves they will become the usual dark Elderwood-leave-blocks in your inventory and you won't get extra snow-blocks from these leaves.
Blue Flowers might grow on and amongst Elderwood Leaves, even rarely on Snowy Elderwood Leaves. And although most Elderwood-trees do not have beehives, some groves might be loaden with a lot of them. In warmer surroundings Rimecones will gather on the ground under Elderwood-trees, on green Grass, Dead Grass and Matted Needles, not on Snow or Snow Caps though. Leafis and Night Leafis can spawn under and on Elderwood-trees too, as they can spawn on Elderwood Leaves placed by players.
Elderwood-trees can be grown by players from Saplings to an average slender size, sometimes without Flowers and most often without beehives. Flowers and Beehives may grow by themselves later on though, and beehives can be grown by players planting Queen Bees on Elderwood blocks.
Elderwood as well as Elderwood Leaves can also be corrupted; Corrupt Bombs, Corrupted Water or Corrupted Wood will turn them into Corrupted Elderwood respectively Corrupted Elderwood Leaves. This will also make them into Fuel of much higher quality.
Unprocessed Elderwood can be used to craft a number of starting recipes in the Crafting Menu or at a Crafting Table in older worlds created before September 2015), like Wood Mining Cells, Processors, Moss Torches