Cactus (Euphorbia acrurensis)
There are many succulent plants commonly if incorrectly known as cactus.
Although not strictly a cactus, the Euphorbia acrurensis shown in the photograph plays the role well in most interiors.
It is not very demanding in average indoor conditions. Just remember the spines (stipules) are sharp.
Photographed in an apartment by Hays Galleria.