海底山（Seamount，又译作海山）是从海底地面高耸但仍未突出海平面的山，所以不能算是岛。典型的海底山由死火山形成，由1,000至4,000米的海底突出。海洋学家定义海底山的独立特征为至少在海底地面升高1,000米。海底山顶通常在海平面下几百至几千米，所以他们被算是深海（deep sea）。全球估计有30,000个海底山，只有少数受到研究。但部分海底山被认为是异常。例如海底山通常在海平面下几百米，但是鲍伊海底山（Bowie Seamount）由3,000米深的海底升高至海平面下24米。

A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface (sea level), and thus is not an island. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 metres (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 metres (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts"