Literally: forest – spread out / gauze – 10,000 – image / elephant
Alternately: All of nature. Everything in existence.
Keep in mind that the number 万, while literally meaning “ten thousand,” stands for any uncountably vast numbers or even infinity. So the latter two characters technically contain the whole meaning of the phrase. The first two characters evoke an image of a vast overgrown forest, provide a sort of concrete metaphor for the vastness, density, and interconnectedness of “everything.”
Notes: Apparently banzou or manzou, while very rare, may also be considered acceptable readings of the final two characters. However, manshou is incorrect.
This four-character compound is taken from the Dhammapada, a Buddhist scripture supposedly comprising various sayings of the Buddha.