Short answers, pulled from the story.
Líf and Lífþrasir are the two humans who survive Fimbulvetr to repopulate the world after Ragnarök. They hide inside Hoddmímis Holt during the great fire and eat only morning dew while flames rage around them.
The noun líf means life or the life of the body as defined by Cleasby and Vigfusson. The female counterpart carries the simple meaning of existence itself.
They hide inside a wood called Hoddmímis Holt during the great fire. Rudolf Simek argues that the wood should not be understood literally but is an alternative name for the world-tree Yggdrasil instead.
This stanza appears in the Poetic Edda compiled in the 13th century from older oral traditions. The Prose Edda written by Snorri Sturluson in the 13th century also quotes the original stanza about the pair hiding.
Their survival represents reduplication of anthropogeny where creation repeats after total annihilation. This pattern mirrors how the first humans emerged from trees named Ask and Embla in earlier myths.