活火山 (huóhuǒshān) means 'active volcano,' a volcano that is still capable of erupting. The word combines 活 (active/living), 火 (fire), and 山 (mountain), making its meaning transparent from its components.
日本有很多活火山。
Rìběn yǒu hěn duō huó huǒshān.
Japan has many active volcanoes.
这座活火山上次喷发是在五十年前。
Zhè zuò huó huǒshān shàng cì pēnfā shì zài wǔshí nián qián.
This active volcano last erupted fifty years ago.
住在活火山附近其实挺危险的。
Zhù zài huó huǒshān fùjìn qíshí tǐng wēixiǎn de.
Living near an active volcano is actually quite dangerous.